A MIG Weld Question

I am doing a fabrication project where I tack weld two 20 gauge pieces of metal together, then cut out, bend - shape the mating part then tack it to the previously welded section.
There can be a 20 to 30 minute span between each tack weld.
Is it OK to just let the welder sit there, powered up or should I shut it down then switch it back on for the next tack. When I shut it down there is a short, 5 to 10 second delay before it shuts down and the the power up is almost immediate, so there is no loss of time to me, just wondering if it was best to turn it on and off as needed or just let it sit powered up through some very intermittent use.