According to passenger Daisy Minahan, Lowe wanted to go back to rescue almost immediately, but a few women begged him not to go.
One of the passengers, namely AB Joseph Scarrott testified that it was only "couple of minutes": "When the ship sank, when there was nothing left of her above the water, he waited, I suppose, about a couple of minutes, not more, and ordered all our boats to row where we last saw the ship to see if we could pick up anybody." (British Inquiry)
Another passenger said, that
"We got away from the ship, and about an hour afterwards Officer Lowe came alongside, and he had his boat filled up, and he distributed them among the other boats, and he said to all the seamen in the boat to jump in his boat until he went back among the wreckage to see if there were any people that had lived…and picked up the remaining live bodies…There were not very many there. We got four of them."
Although it is a bit controversial, I assume it was about 1-2 hours, until he went back.
I highly recommend reading this website by Dan Parkes. His work is truly amazing.
Titanic's Officers - RMS Titanic - Fifth Officer Lowe
Best regards,
Bailie