Need a separate time tracker for contract-based hours, similar to pre-pay hours in customer's details.

For example, our contracts include an xx amount of remote and on-site hrs on monthly basis. I created Line Items called Monthly Remote and Monthly On-site to assign them within the contract page, and to track them within tickets. So if the customer has 10 remote and 3 on-site hrs, how do I go about tracking usage for both on the customer's details page? The only workaround I found was to go through each invoice per ticket, and manually calculate time used per line item used. However, some customer's have 50+ tickets a month, and doing it manually will be a huge waste of time.