We currently do not have plans to add a custom "sleep goal" in Garmin Connect. We apologize for any inconvenience this may cause.
+1 to this problem
It is very important to be able to get a tick for the number of hours we sleep. After all, unless we get positive reinforcement from a gadget, our lives are useless. Disregard it’s the quality of sleep that counts, not the length; there’s no target for quality so it can’t be important.