For every park?
It will say that when there's not a bus currently dispatched to that resort for that park. As soon as they dispatch a bus and the GPS sends an update, it will update with an arrival time
If it's for every park then it may well be having an issue linking with the GPS system at the moment.
I've been wondering if it was broken in the app too. I have a feature on my site that taps into the bus times system and it's been broken for several days now. Haven't been able to confirm it was broken in the app since I'm not staying.
I would suggest you don't trust the app or the screens at the bus station too much. A bus might show up unexpectedly at any time, and your scheduled bus might be re-routed or delayed without warning.