You don't need to open the system so you don't need the vacuum pump at all?
If the system has valves and ports in the right locations....
use a recovery machine to pump the condenser into the receiver, stop at about 2 psi. Braze the leak. Open the valves. Top up the system. Hand them a bill.
No vacuum pump needed, and down time of less than an hour.
I've fixed leaky condensers a few times like this, and evaps dozens of times (those are really easy since you can use the compressor to pump down.
No vacuum pump ? I've heard of people pushing the air out of the other valve when they release the gas , and close the valve when you think all air is gone ... is this what you do ??