OK, here's the deal. When your co gets notified to do a certain amount of "randoms" they really don't care if you are "on duty" or "off duty". What happens is, THEY are notified to have 10 randoms done between june 1 and june 4, for instance. So, they then send out the notifications to the 10 drivers to go "immediately" to a testing station, right ?
The problem is, not all drivers are on duty at that time. Some will be but some may be home on "time off" and some my be on a "10". rarely have I seen a driver get called for a random at 3 am. Why's that you say ? because testing stations aren't open at that time. Most are 8-5 M-F !
One co I worked at said do a random by next Friday ! Yeah, OK Boss, no problem. A random is a surprise supposedly, but in reality, co's are notified a week in advance.
So I would say do not make yourself available when "off duty" just to play it safe. Jimmy