The app most likely came from sleep mode and you are most likely seeing "SeriousMD is Offline" in the bottom status bar.
Sync happens instantly when the Internet is working and the app's status says that SeriousMD is up to date.
The most likely scenario that happens when sync takes "a long time" to work is when the device is left sleeping for a long while (the screen is off, so iOS will conserve battery by disconnecting from Wifi, hence disconnecting SeriousMD).
Thus, when you open the device and app again, it will take a bit of time to connect.
Normally, it will take a few seconds to connect to wifi again, then 30 seconds for the SeriousMD Doctors app to try and sync.
So whatever data was added on that device, it won't sync until it connects.
If you cannot wait 15-30 seconds, try closing the iOS App by pressing the home button twice and swiping it off, and then opening it back up.
Once inside the app, it will connect instantly to our servers.