Lastly, keep in mind the more time you have, the more you tend to waste, so
while you may feel rushed at times, consider how quickly you can really do the
job while still covering all bases - sometimes we work better under (reasonable)
pressure.
Parkinson's Law IIRC
Try this - give yourself a time limit to plan the flight (say an hour). Then spend the first 5 minutes prioritizing the planning tasks and then do them in that order. Stop after the hour. Go fly.
Or at least try a time limit for yourself and see how you get on, even if for a practice. The time management discipline that is required to do your planning in a reasonable time is one of the skills that you need to develop. Your instructor should help you with this - but you can work on it too anyway.