A piece of personal advice: Given a list of tasks varying in complexity, do the the hardest one first.
You'll be able to quickly figure out how long it takes to finish those easy ones because even from just looking at them for a few seconds you'll understand what's required. Perhaps you'll even trick yourself into thinking you can knock them out of the way, quickly enough that it'll leave you ample amounts of time to address the harder tasks.
But the hard tasks will have unanswered questions. And answering those questions might involve asking new questions. All of this will take time. It may be that at some point during this process you realise you don't have enough time to complete the other tasks at all. That's fine, because you're in a position to do something about it.
And lastly, often solving harder problems leads to a greater payoff, giving you momentum you didn't have when you started and allowing you to finish the easier tasks in less time.