Does the wake back to bed method work all hours of the day or just nights and mornings? 
The only time it doesn’t work is when falling asleep puts you to a long NREM stage. It works at any time of the day, but depends on your sleep schedule. When you take your core sleep, which is a longer period of sleeping, no matter when that is, cut it short and perform WBTB near the end of that. If your schedule is several short periods of sleep, aka polyphasic sleep, you mostly get REM and don’t have to worry about WBTB.