In reply to Steve John B:
I'm fortunate enough to have been in this position for a couple of years as I changed to compressed working hours (5 days into 4.)
Generally, I go walking, ride my bike, do chores to free up family time on the weekend or go on a little day visit to a museum or exhibition. Sometimes, I sleep in and laze about watching TV!
It's handy as if the kids are ill or on holidays, I can juggle my day off to suit.
Enjoy it!