The shuttle bus leaves Lowell at 0830 and leaves JP at 1430. It requires advanced reservation through the Lowell VA. The schedule is at https://www.boston.va.gov/visitors/shuttle.pdf
I'm not 100% sure because it's been a while. However I believe it leaves 7:30-8:00 A.M. and returns depending on how many folks go. Once everyone is done with thier appointments it makes it's way back. Unless it has changed you maybe at JP for a while.
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