Sounds like you work 7 days a week from what I read, surely this cant be true? Would have thought the working time directive allows you time of? Max 48hrs per week and all that?
See if you can get a copy of your work rota a few weeks in advance and then book the lessons around the days you know you are off work
Im a PAYG student who normally flies on weekends only but I always try to get evening slots while the lighter nights are around. The wind is minimal around these times (6-7.30pm-ish) and most of the commercial traffic is out the way so less time spent in the hold burning a new hole in the wallet
At the end of the day, it's not a race so just make sure you spend your money well and learn as much as you can rather than whizz through the syllabus and then scratch your head when your PIC because you cant quite remember how to deal with a certain situation properly.
Just my tuppance of input. Good luck with which ever way you go and have fun! Flying should be fun not a chore