I wish I had a job where if I completed all my work quickly, I was allowed to do whatever
How do they know if you're done, if you haven't "turned it in" yet? They're probably not watching your screen constantly.
My last boss told me essentially (paraphrasing), "I budget time for your tasks. If you finish late, I look like I underestimate time required, or you're not up to it. If you finish early, I look like I overestimate. If I give you a week to do something, I don't care if you finish in 5 minutes, don't give it to me until the week is up unless you want something else to do."
Sounds like your last boss was working under some very twisted incentives.
He was told to have our team do 'x', and either given a deadline, or asked for a timeframe it would be done by. Then he assigned it out to the team.
We certainly did not receive bonuses based on doing work faster, so unless you are, what incentives are you being driven by to do the work sooner?
That is really not the norm nowadays.
Was it ever? Twenty years ago I had a boss that told me he cuts every estimate engineers give him in half and the work always gets completed on time, never mind the terrible quality and massive amount of bugs.