To rootcause this problem, you need to first diagnose where the problem lies i.e. Client(laptop) or Access Point(AP)
Have you tried connecting your laptop to another Access Point(not Meru brand) with similar security and tested if it remains connected with that AP for more then 5 hours?
What OS? Please try to upgrade to the latest driver 188.8.131.52 driver/SW which might solve the issue you're facing.