I started an office job once and naively believed I could do this with the TOIL system. I was the last out most nights for my first few weeks. My time sheets were jam packed with accumulated TOIL. I was excited by the prospect of extra long weekends, but then told that flexi time in fact means just staying late unpaid for overtime when they decide, and taking days off when you don't want them. They'd phone on Sunday to say don't come in tomorrow, take a TOIL day.