Data connection takes a long time to start up My tablet has a SIM card that gets data over AT&amp;T's cell network. Once the connection gets going it works great, but connecting to the network takes about 5 minutes. This is strange because it only takes a few seconds for the tablet to determine that it can detect the network at full strength; it just takes a long time for the little "H" to show up next to the signal-strength icon, at which point data exchange can occur. 

What can I do to accelerate this? I'm running CyanogenMod on a Nexus 7 2012 tablet.
Reason 1 :
H (HSDPA) signal requires greater strength and a mobile tower that emits 3G (HSDPA) signal. In your case ,the phone connects to a 2G mobile tower (near your vicinity) and then searches for a 3G signals ( maybe that tower is somewhere far)

Reason 2:
Cyanogenmod maybe designed in such a way that it first connects to 2G and then swithces to 3G. You might want to head on to their support page for further information.