The default app pool setting for the SharePoint Central Admin site is to recycle at a set time each day. 

Given that most of us rarely use Central Admin more than once or twice each day (because we script all the changes to the SharePoint farm configuration, don’t we?  Don’t we??  Ok) we don’t like it when you hit the CA url and it’s takes ages for the site to JIT compile.  Because the app pool recycles every night you’ll take the hit every time you hit the site for the first time in a day.

Solution: Don’t recycle the Central Admin app pool. 

1. Browse to IIS Manager (Start >> Run >> inetmgr)
2. Expand the “Application Pools” node
3. Select the “SharePoint Central Administration v3” app pool
4. Edit Application Pool Recycling Settings
5. Uncheck the Specific time(s) box

Test it yourself.  Decide if it’s something you should configure in your own SharePoint environment.