How to drop out of airplane/flight mode periodically to check messages
There are multiple automation tools which most likely can do this for you. Some of them, especially in connection with your real concern, are listed in my answer to What is Cell standby and how can I keep it from eating my battery?.

Aside from that, and you might wish to check helpers like JuiceDefender, Easy Battery Saver, and GO Battery Saver &amp; Widget. Amongs others, they do exactly what you asked for: toggling airplane mode or rather the data part of it, to enable apps to sync only in defined time frames.