It's easy to calculate the amount of seconds between two points of time with scripting, so in my opinion this would be added bloat. If anything, I'd propose the addition of a new switch '-u' to /timer, which allows you specify a CTIME value. But once again, this is easily achievable in scripting.
Also in my opinion, having persistent timers would be a waste. Timers are for scripting, and ON START *is* scripting. It's not a trivial chore or challenge to start a timer with ON START, nor does it come at any realistic cost whatsoever. If ON START didn't exist, I'd endorse this. But unfortunately it's more than completely feasible to achieve the same outcome using the current method of persistent timers.
