My iMessages on iPad 2 work only part of the time .

My iMessages works intermittently. It work fine for days, then has a few hours where it will not deliver messages. I have a wifi connection, not phone connection. My husband's iPhone works fine using the same wifi network whirl I am having trouble. I have tried resetting, turning wifi on and off, reconfiguring the network connection, a full restore, turning off iMessages and on again, etc. nothing fixes it. It will suddenly start working again, usually late at night. Ideas?