With GenCG 5.5 and above, Resident Clocks will continue to play through the duration of your Page List sequence, regardless of what the Run Mode is set to.
You can insert a Resident Clock by going to Insert -> Resident Clock.
If you are using a single-channel system running GenCG 5.0 or below, the clock will cut off and on with each page played. For the clock to permanently be on-air throughout your page playout sequence without interruption, a new Compix system is needed running GenCG 5.5 or above. You can also achieve this with a dual channel Compix system.