I don't know much about FRMS stuff, but rest is always prospective in nature, so you have to know about it before it starts. If you were on a single 24 hour day off, and ascertained at midnight that you were back on rest for 24 hours, that isn't 1 block of 48 hours off. It's 2 different 24 hour periods free from rest. They can't just tack on 6 hours and call it a 30 hour rest period, just like they can't call you in the middle of an overnight if you blocked in late and extend it by 20 or 30 minutes so you get a full 10 hours. The full 10 hours would have to start over in that case.