Finishing multiple timers for the same task causes time remaning failure

[OwenPattison]

Problem:
Given a list a timers to finish if you have multiple timers for a single task when you add time remaining it does not take other given values into account, leaving us with duplicated time remaining.

Proposed solution:
When starting timers we could check if there is an existing timer for the task and then add additional time (if any) to the previous timer.