The current system for setting timers on explosives is not very carefully implemented. You can only add 40 seconds at a time, and as soon as you've added any amount of time, the clock is ticking. Instead, the time should be set (by a much cleaner method, perhaps a dialog or a field to type in minutes/seconds), and then should be able to be started and stopped. This would also allow for the other team to have a chance to defuse the explosive.