If you want to be time efficient - don't go to the gym!
If it takes 15 minutes there, and 15 mins back - just spend 30 minutes doing exercises at home!
Get fit and save a lot of time.
Of course, that old discipline thing needs addressing...but apart from that, 90% of the things you need are right where you are...
The gym is close by and at the moment, we don't have the discipline to work out at home. it is okay in the summer to go for a run and do some tabata intervals outside but, Winter is coming.