Most companies that I have ever worked for had a 12 hour standby period.
In the event of a call-out then half of the time already spent on standby counted towards the subsequent duty.
I hated standbys whilst down the route but I never minded home standbys. I always reckoned that the days at home when I wasn't called out were a bit of a bonus and were an opportunity to do all the jobs that the Family Controller had been bitching about for months and all done in company time!