From the Winboard help file:
/clock or /xclock, or /clockMode true|false
Determines whether or not to display the chess clocks. If clockMode is False, the clocks are not shown, but the side that is to play next is still highlighted. Also, unless searchTime is set, the chess engine still keeps track of the clock time and uses it to determine how fast to make its moves.
So in the start up dialog box you could put a check mark next to the
Additional Options box and add
/clockMode false in the Additional Options field space. Not sure if it would be /clockMode false or -clockMode false, but /clockMode false works for me. (Make sure you use a capital M. In other words, watch the spelling.)
Or you might be able to add this to the winboard.ini file for the engines or engines you use, that is if you never want to see the clock. Adding it to the winboard.ini file, in the appropriate place, will prevent you from having to add it to the start up dialog box each time. Someone else will need to tell you the appropriate place in the winboard.ini file to add it.
May be H.G.Muller, or someone else, knows a better solution or trick.