Regarding time limit, you can only limit it within a range of 1-3600 seconds. Trust me, that's more than enough.
*SERVER*\oxide\data\RealPVE\MonumentsConfig.json
But if you just want to disable tracking(loot available to everyone) for a monument or multiple monuments, you can either disable it for all at once or disable specific monuments.
To disable specific monuments, you need to list their IDs in the property named "List of IGNORED monument names. Example: powerplant_1", for example: "powerplant_1", "harbor_1", etc.
If you want to disable all at once, you can either remove the MonumentsWatcher plugin(if no other plugins depend on it) or delete all tracked categories in the monument config file under the property "List of tracked categories of monuments".