Hi Donna,
The most common problems are:
1) Your device is not connected to the Wi-Fi network. Make sure that the little upwards "waves" are on the very upper left of your screen.
2) On the device (iPhone, iPad, etc.) Time Master must be *running* and it must be *awake*. That is it has to be lit up on one of the Time Master screens.
If all of those are ok, you may have to restart your Wi-Fi router too. Just unplug the power for 30 seconds, plug it back back in and wait a minute or so for it to completely start back up again.