Power on, white screen for 1 minute then login screen - not sure?

Hi. I have searched the forums and not sure which solution applies to what is happening. Have read 75 posts/ reports with macbook air since 2011 about "boot up", "boot screen", "login issues" "slow to boot", etc., etc.

Not sure...

I have "shut down" all the way in the case I am describing. Mac stays dormant for whatever period of time. Open screen. Hit power button. Turns on. White screen for 1 minute plus - sometimes longer. Sits there. Used to be quick to prompt for login password. Now is taking a longer time about once per week increases in duration.

After I login, everything seems to be fine.

What technique, fixit or what not do I perform? Thanks to all!

Macbook is about 4 years old.