I will break down the different parts in case someone only can help me with different parts.

1. In Zoho crm is it possible to create a visual window that shows remaining time left?
For example the costumer has 5 hour free costumer service so somewhere in the in the costumer record in a module (Contacts/costumers) i get to see the number 5.

2. When i logg a call and the call takes 45 minutes two 30 minutes is removed from he 5 hour total so the free hours left is 4. The increment is 30 minutes because the costumer pay for each 30 minutes that begins, meaning when the call starts that is counted as the first 30 min as son as it passes 30 minute mark a second 30 min is charged.

2a. If its is easier i could also use a drop-down with ten  30min, so whe the call takes 45min, i select 2x 30 min.

Im not a coder, sorry.