You're already undercharging on your "door rate", $100 an hour is about minimum....Even in the rural South!!!! By giving away parts & labor on top of that....You're burning the candle at both ends.
People can wait, I make it a point not to promise anything the same day even when I can easily do it......If one want's instant gratification, They're at the wrong shop.
We need to take in consideration how flawed "Book Time" IS.......Toyota pays really good, FCA/Chrysler usually pays less than actual time. I adjust these to maintain a 125% efficiency rate. Honda, Ford & GM labor times generally hit that spot on. I'm not going to hit a Toyota owner for 8 hours when it takes 4, And I'm not taking a bath on a FCA/Chrysler vehicle because they like to screw their dealer techs.
I want you to succeed, Not just scrap by. There's a balance/symmetry to be found here but it's unique to every situation/location/customer base.
I did side work when I was working my regular job, But never tried to run a shop after hours. I simply decided to spend my life savings & most of my retirement fund on building & opening my own garage full time. Best decision I ever made as I paid myself back in 18 months.