Why do you have to have the vacuum on for the entire process. What happens if you draw a vacuum and shut is down and leave the blanks in the juice to save ware and tear on the vacuum.
First, if you are using an oil filled rotary vane pump as recommended, don't worry about the wear and tear on the pump. They are made for continuous use and are not harmed by running for many hours at a time. The reason to keep the pump running is to keep the air moving from the wood. You are only creating a vacuum in the empty space above the blanks. If you close a valve and shut off the pump, the air coming from the blanks moves to that empty space and the level of vacuum starts to drop. If vacuum level is dropping, air flow is also dropping. You may not see it on a typical gauge but if you use a precision, micron gauge, you will see the vacuum level start dropping immediately after shutting off the pump. Think of it this way...place a straw in a coke and start sucking. As long as you are sucking on the straw, the coke is flowing. If you suck on the straw enough to get the coke to the top of the straw and then hold it, the coke stops moving. The same thing happens in the chamber in simplistic terms.
Keep the pump running and you will reduce your amount of time under vacuum compared to pulling a vacuum and then shutting off and holding it, then starting again, etc. Maximum continuous vacuum equals maximum continuous flow of the air from the wood and reduces the time to get the air out. The more air you get out of the wood, the more resin you can get back in when you release vacuum and allow the blanks to soak.