If you only have time to check once, I think between 10AM-11AM Philippine Time is a good option. I've read that sometimes they randomly open up slots during the wee hours (like 3AM), but I think 11AM would still be okay since I was able to book at 12:41PM.
I also think they open slots for both biometrics and interview at the same time, but the interview slots get snatched up more quickly--probably because there's higher demand. You don't have to worry about opening another site though! When you book your biometrics first, you just have to wait a bit for the site to redirect you to the interview slots. It looks exactly the same, but instead of "OFC MANILA", it'll be "Manila IV" if I remember correctly. In the off chance that you only book your biometrics schedule, I think you'll be able to book your interview on a separate date when they release slots again (maybe this is the reason why the number of slots for biometrics and visa interview are not equal).