Silence is not a no
A customer who read your message and did not answer has usually not chosen someone else yet. They put the phone down. Treating that as a rejection is the most common and most expensive misread in the whole process.
Three touches, spaced apart
A workable rhythm is short and front-loaded: one after roughly ten minutes, one after an hour, one the next day. Beyond three you are no longer following up, you are pestering, and the fourth message costs you the goodwill the first three built.
Every one of them stops the moment the customer replies. A follow-up that arrives after someone has answered you is the clearest possible signal that nobody is reading.
Each message must add something
"Just checking in" is not a follow-up; it is a request for the customer to do work. A useful one adds a concrete time slot, a relevant detail about the job, or a single easy question.
The last one should leave the door open without sounding desperate. "If the timing is not right, no problem — we are here when it is" closes more later work than one more push.