The amount of days to not repeat a quest is in the get_random_quest script, but each one is set individually - so you'll have to change each one that you want to.
Just open the scripts.txt file and search for
2133 2 1224979098644774938 (the first one is in the appropriate script). The first one you'll find will have a
0 following it, that's where the variable is initially set (so don't change that one). I'll list the results you'll find, with the default number so you can find the ones you want to change. These numbers are the number of days it takes before the quest will repeat.
1. initially set, 0
Village quests:
2. village grain delivery, 20
3. village cattle delivery, 20
4. train villagers against bandits, 40
Mayor quests:
5. Deliver wine/ale to town, 20
6. troublesome bandits, 30
7. kidnapped girl, 30
8. move cattle herd, 20
9. persuade to make peace, 100
10. deal with looters, 30
11. deal with night bandits, 15
Lady quests
12. rescue prisoner lord, 73
13. deliver message to prisoner lord, 30
14. duel for lady, 50
Enemy lord quests
15. Lend surgeon, 50
Lord quests
16. Meet spy in enemy town, 50
17. Raid caravan to start war, 100
18. Escort lady, 30
19. Raise troops, 15
20. Collect taxes, 20
21. Hunt down fugitive, 30
22. Kill local merchant, 30
23. Bring back serfs, 20
24. Follow spy, 50
25. Capture enemy lord, 80
26. Lend companion, 30
27. Collect debt, 20
28. Incriminate loyal commander, 180
29. Capture prisoners, 20
Just go to get_random_quest and start searching for 2133 2 1224979098644774938, all the instances you find should be followed directly by the number on that list. Then just find the right instance of it to edit for whichever quest you want to repeat more often and change it. This is savegame compatible.
Have fun.
-edit- If you're looking for the caravan quest, the reason it isn't in the list is it doesn't have a repeat timer. If for some reason you want to add one (maybe you don't LIKE caravans, and want to limit it to once a year or something) see the bottom of
this post. And by doing this, further my evil plan to take over the world! Mwahahaha.