5:30-7:00: These are the usualy oracle timings of when the 1st oracle will arrive in your base.
6:00-7:00: These are waprgate timings
7:30-9:00: These are your blink timings
Oracles: Look for either gas 1st or double assim before core, Gas 1st can be tricky but only if you don't know what your looking for. So if you see one gas and a gateway that looks like its a little delayed for an average 13 gate click the gas, you should be doing this out of habit anyways, and see how much is mined if its a rather large amount over 100 or more than it was probally gas first as that Assim should of been place at 15 supply for a normal gateway expand. The next thing you want to look for if you see gas 1st or double assim are proxy pylons or pylons around the edge of bases. Use your reaper to check for an in base stargate and on smaller maps use it to scout around usuall proxy positions, on large maps use a single marine to scout around your side of the map for a proxy while using your reaper to scout their base. If your scouting is denied scan their base around 5:30-6:00 and if you see no twilight or stargate and are completely in the dark you can still relly on the timings.
Twilight: Once against your looking for either gas first or double assim along with trying to confirm the twilight counsel. If you are able to confirm a twilight counsel then you want to make sure you see it researching blink other wise theirs a high likely hood their will be DTs. Once again you use your reaper and a marine as well on large maps to check for proxies and use a scan around 5:30-6:00 if still in the dark. You can also relly on stalker count to help confirm an blink all-in, if your able to scout that the Toss went up to 3 stalkers instead of just 2 their is a high likely hood of a blink all-in.
Gas timings won't be all that effective in scouting a warpgate attack, even though a classic 4 gate has only one gas taken. What you want to 1st look for is gateway timing was it an 13 gate or a faster gate ranging from 10-12, then you want to check for chronos on the cyber-core, and lastly the most telling gateway numbers. Remember just because you see 3 gateways before or right after they expand it doesn't mean theirs an early gateway attack coming, however if you see more than that then it is almost always an attack or its just inefficient. So if you can confirm an early gate then be ready for some sort of early rush rather its an; early MSC, zealot stalker, or some fast tech. Still you can relly on your timings around the 5:30-6:00 mark be closely checking their army size , and gateway counts either with a reaper or scan.
How To Hold:
Oracles: Holding an oracle attack comes down to positioning and not over reacting to some minor scv losses. Remember the Toss sacrificed his eco to go oracle and will need a decent amount of kills to stay on even footing with your mules. Furthermore, you should be aware no matter what that some sort of tech is coming your way if you were able to scout gas first or double assim. Which if you were able to scout either you should always have placed down an engineering bay so you have the option to place down turrets for either detection or for oracles. The next thing is if your not planning on being aggressive its always a good idea to rally your marines into your main mineral line between 5:30 and 7:00 minutes anways, just remember it takes more than 5 un-upgraded marines to kill an oracle. WMs can also help out alot against oracles, but placement is key as even burrowed a keen eye can see them as a dark spot on the ground. The best places to put them are, around assims as they will be blocked from view and you can use marines to bait oracles over them if you have to. Just don't go crazy with turrets 1 in each mineral line right in the middle though, and eventually one right by your production. Other than that don't worry about moving out on the map to destroy a proxy stargate until you have fortified your mineral just send out a reaper, scv, or marine to locate it force either an oracle or unit over to defend it then go kill it later. Also be aware of what their follow up is make sure they one have expanded and 2 what their follow-up tech is. You will want to know rather its an oracle 4gate, voidray all-in, pheonixes, or normal robo play. A side note if you see more than 1 oracle they will not have a large ground army at home and are completely relliant on getting damage done so by simply denying them damage you are already miles ahead, two have a small WM drop if you went for WMs can work wonders as you will draw at least one of their oracles back and force it to use up its energy for detection, along with a high likely hood of getting a good amount of probe kills.
Twilight: With the recent patch holding a twilight all-in or opening is relatively easy especially with WMs and the new maps. If you scout double assim or gas first be on the look for their stalker count and or a twilight counsel. Once a twilight all-inn is confirmed their are a number of ways to hold it. First if you went 3 rax and concussive shell like polt having a small force, 8 marine 1 marauder with slow, out on the map will help hunt down and kill any stalkers caught out on the map and or allow you to counter attack shutting down their production. Second if you went for WMs simply drop their base they will most likely have nothing in the way of detection and you will be able to slow down if not shutdown their eco while defending with a few bio units and well placed WMs at home, don't worry about pulling scvs in this case as even if you lose a few you will still be on higher economy. Thirdly having medivacs and or stim out should allow you to defend just fine along with some well placed bunkers 2-4 depending on the map, with 2 at your natural entrance and 1-2 in your main. On some maps you will need none in your main as their is no way to blink into the main without going through the natural.
Warpgate: Holding these off is really about Build-Order, Scouting, and Micro. Opening with a reaper expand into a 3 rax with a small force with a marauder with slow in it is a great way to not only put on pressure but shut these types of attacks down as Stalkers can no longer out micro your pre-stim marines nor run away. Other wise Having WMs can also shut this down along with allowing you to counter attack and or backstab and win. If all else having a well placed bunker at the top of your ramp and or a supply depot rax wall with scvs and Bio forces can hold quite well against this too, just don't be afraid to lift and give up your natural remember their on 1 base too and you have mules.