Turn on account for N hours

I think I will use this service for when I am on the road, away from the Internet. A typical scenario is a trip downtown to a meeting / party. I would then turn sms on when I leave and turn it off when I get back. Usually I know approximately how long I will be gone, so it would be nice to have commands like this:

d tweet2sms Account On 4 (turns on account for 4 hours)
d tweet2sms Account On Today (turns on account for the rest of the day (which ends at 3am of course :-))

If terms of direct URL's (if you get around to implementing that), this would be something like:

http://tweet2sms.com/on/4
http://tweet2sms.com/on/today

Sjors