First logon of the day for any user takes extra time to enumerate the Applications\Desktop. Subsequent logon for the same user is quick.

First user logon after a IIS Application pool recycle will take extra time to enumerate the application as cache is cleared on Storefront.
This behaviour is expected by design.

Problem Cause

Storefront SF caches the app details in memory. IIS application pool has an auto recycle setting which will recycle the application and clear the cache based on the Application pool recycle configuration.

Refer to IIS documentation Periodic Restart Settings for Application Pool Recycling for more details on configuration options