I'm going to assume this is BW, and not BW2.
Delay and timer0 are different things, the former being a time offset and the latter being a parameter tied to your DS + cart combo. Neither should change now that you're breeding instead of wilds/stationaries, so the values you used before should still work here. By delay I'm assuming in this case you're talking about the offset you found while calibrating, where, as you said, you have to start the game earlier than your target time. In the case of a original DS/DS lite, typically this is ~1 second (iirc DSi are ~5-6 and 3DS are ~8). So far starters, I'd say keep using the values that you used when you were successful; nothing should change here.
Possible issues that can cause this include starting your game at the wrong date/time, getting the wrong Timer0, not using the proper keypresses, not using the parents you think you are (i.e. different IVs from what you entered, using foreign language parents when you think you aren't/vice versa), improper setup of the tools, and not hitting your correct frame. I'll gloss over most of these because you seem familiar with the process of RNG in Gen 5, but do confirm that these are being entered/done correctly. If you'd like to post screenshots of your tools I'd be happy to take a look, as well as if you have an example of something you aimed for but got instead.
My guess is you are hitting the wrong frame. Unlike wild and stationary mons, the IVs are tied to the PID frame when breeding. So if you hit the wrong frame, you'll get the wrong IVs. There are NPCs on the route, so your best best is to open the menu ASAP, do your chatot advances (I like to assume the NPCs advance ~7 frames as a starting point), then immediately accept the egg. Hatch it, and look for the frames around your target to try to identify which one you hit, then adjust on your next attempt. You probably won't know the IVs, so try to match it up based on the characteristic + gender + nature.
edit: also if you haven't already, I'd recommend checking out our onsite guide to the process: https://www.smogon.com/ingame/rng/bw_rng_part5
If videos are more your style, im a blisy is usually a go-to