Do you have any ideas, including guesswork, about where your hurry is coming from? For example, are you in a hurry to go do other activities? Are you stressing about how many problems you have left in your problem set? Do you feel as though you're stupid if you don't immediately see the answer?

Some strategies that might help, depending:

1. Block off time, know and visualize that this time is for proof-writing and nothing else (you have this block of time whether you use it or not, and cannot move onto other activities), and visualize that this is the only problem in the world.
2. Make a plan for the rest of the day (and write your “must hurry to do” activities down on a list, with their own timeslots) so that you can believe the blocked off time in 1. When your brain tells you you have to hurry and do X, remind it that you’ll do X at 4pm (or whenever), that this is the timeslot for proofs, and that focusing slowly will get the most done.
3. Find a context wherein you have the sort of slow, all-absorbing focus that would be helpful here (whether on proof-writing, conversation, or whatever else). Try to understand the relevant variables/mindset and to set up the outside context similarly, and/or copy your internal frame or stance.
4. Think of great performers who were utterly absorbed in their tasks, and of the excellence they embodied. Put up their names, photos, or other priming influences. Visualize yourself as embodying that same mindset.
5. Use “positive self-talk” to prime yourself as you work, by saying things like “I am moving slowly, with full focus. I am noticing every nuance I can notice. My mission is to do well, regardless of speed.”
6. Do your proof with a friend or a student, while showing them what patience looks like and talking about how you’re learning patient, focussed mindsets.