If you do not charge for your time than its a hobby, else charge for the complete job that includes the time to program and set up, clean up and put up. And if the call to run both machines at once to meet a customer set urgancy than the charge for the set up of the second machine pluss a $$ for the shorted time.
Think of it like this you could run two difrent jobs for two difrent customer at the same time with two difrent machines. So you would charge both customers for there
parts, not give one them parts for free.
Machines cost pluss electric and floor space and tooling else every one would have two or three machines themselves.
Always charg fair for all the work you do.
As a boss i had once told me, he could go broke at the lake he would not have to work at going broke.
John