You can WILD in 5 minutes or so if you utilize Wake-back-to-bed or morning slumber. The 90 minute cycle is when you are going to sleep in the first place, that is why it is generally quite hard to WILD straight at the evening

I do that a lot. You just need to have good knowledge how your sleep pattern works or then just doing it by pure luck ^^ if I wake in the middle of REM-cycle, I can go back with WILD in about 5 minutes average.