Juneau - ziplining

We have booked a dog sledding trip with Coastal Helicopters that also stops a second time for a short while to see the glacier. This takes place in the morning and then we have all afternoon and evening in Juneau. I would like to book a ziplining in Juneau in the afternoon but wary to do this just yet because

(1) if the weather is not good enough to set off for the glacier at the scheduled time, we may set off later and not be able to go ziplining

(2) if after the morning we feel tired, we may not fancy another tiring excursion.

Has anyone seen at the dock excursion companies selling ziplining for that day, especially in the afternoon? I would ideally like to see what happens with the helicopter trip before booking the ziplining.