Hi,
Personally, set a suitable time for Application Pool is helpful. Application Pool recycles is used to release memory, get rid of potentially crash and improve performance. But when Application Pool recycles, ASP.NET state will be lost.
The good recycle time is that we don't get the crash during Application Pool is running and user state is lost least. To get this balance time, we might need to do more test or check logs. ASP.NET Health Monitor is good tool.
In your case, you can configure it basing on your requirement, such as memory pressure.
For more information about Configuring Worker Processes for Recycling, see http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/f11b8294-cc42-4e9c-8482-6257bf3b80f2.mspx?mfr=true
I look forward to receiving your test results.