There's a Hold Time for conventional frequencies, how long it stays and scans all channels in a department and a 0 time scans all channels only once.
For trunked systems the Hold Time tells how long it stays on the control channel trying to decode the data and find an active call. It always stays a minimum of 1,5 sec even if you set the timer to 1 or 0, if there's a carrier on the frequency that opens the squelch. If there's no carrier and no signal then it just stays 20mS on the control channel frequency and then goes to all other frequencies that are programmed in the site to try and find a control channel signal.
/Ubbe