Have uploaded approx 70 360 spheres and my stats only say 16 Google Maps approved photos.
Most of them are done with a Theta Z1 23mpix camera. they are between 15-28 mb in size.
All follow the minimum requirements.
How long does it take to get them approved? Thought it was instantly.
If you check on your profile, you will probably see that each single photo appear as “approved” but on your statistics the number is lower.
This is because the info attached to every photo are related to the basic requirements (size and resolution) while the final approval is checking the photo itself, quality and contents. Normally to me it was taking 24 to 48 hours, to have my photos approved.
After that, you will be able to switch ON the available for hire switch
It just took some time 
61 approved now 
"Available for hire" switched on
Thanks for taking time to answer/write me @ErmesT 