FILD on low sleep

I know FILD is best attempted after a full 5 hours sleep or so. But if you only have time for 4-5 hours of sleep, this would probably be the best method to wake up an hour early for no? After all, you don't need to be seeing imagery, you just need to be really tired right?

No.
In order to LD you must have already entered your REM cycle.

If you wake up and remember a dream, then that is enough.
If not, then it isn't enough.