I had this question too… then I realised it’s a bit irrelevant.
If you’re offering a high-demand, general service like web design then I guess you can easily get thousands of impressions before you get work.
If you’re offering a niche service like editing academic papers in astrophysics, I guess you’ll get far fewer impressions before you get work.
I think it makes more sense to look at the relative changes in the number of impressions for the same gig over time. And also run several gigs that may be mostly similar but have one fundamental difference. Then you can compare performance over time, and get a feel for what works in your service niche.