For some devices, the "Try Later" prompt may appear frequently if the Apple Watch is low on system resources. In testing, this occurs more on first generation Apple Watches than others, though it's not unique to this model of Apple Watch.
Trying the following methods on your Apple Watch may free system resources for a more efficient analysis:
Force Quit Sleep Pulse
If Sleep Pulse is lagging or not providing a complete analysis, force quitting the app may reset the memory. Once you have pressed "Wake", your motion data will be saved until you start a new sleep. Using Sync Again will allow you to still analyze your sleep even if you force quit or restart your watch.
Apple Watch: With the app open, press and hold the side button to show the power options. Then, press and hold the Digital Crown to force quit the app.
Perform a soft reset by holding down the side button and the Digital Crown until the screen turns OFF and back ON with the Apple logo appearing. This is usually the best method to free up the system memory or processor for sleep analysis processing.
Motion & Fitness
Under Settings -> Privacy -> Motion & Fitness. Toggle OFF and ON the switch to reset the permission.