The 26-year-old Lidl–Trek rider took advantage of dry roads to cover the 28.6km from Lucca to Pisa in 32:30 seconds for his first Grand Tour stage win.
By the time the leading riders left the start gate rain was falling, making the corners slippery and reducing speeds.
Del Toro (UAE Team Emirates) finished in 37th place on the day but crucially avoided any mishaps on the greasy surfaces to stay in the leader's pink jersey.
His general classification lead over Juan Ayuso was cut to 25 seconds, though, as his Spanish teammate put in a strong showing to finish 22nd in the time trial.
Overall favourite Primoz Roglic, bidding to claw back time lost in a nasty crash on Sunday, finished 1:15 down on Hoole's time but made up ground in the GC battle as he finished 17th. The Red Bull Bora Hansgrohe rider climbed to fifth overall, 1:18 behind Del Toro.
Slovenian Roglic had crashed in a pre-stage inspection of the course on Tuesday, but after his problems at the weekend, he is very much back in the hunt at the top of the leaderboard.