Not long. Looking at Walcotts record he lost to any to HW he faced.
He is also listed a 5 ft 11. 74 inch reach.
Wilder is 6 ft 7 . 84 inch reach
That 8 inches in height and a 10 inch reach advantage
Wilder by KO inside 4 rounds
I do consider Walcott better than everyone except Stiverne on Wilder's resume, so I do think Walcott would last about half the fight. But I wouldn't be surprised if Wilder destroyed him faster.
How long would Walcott last against Wilder?
Not long. Looking at Walcotts record he lost to any to HW he faced.
He is also listed a 5 ft 11. 74 inch reach.
Wilder is 6 ft 7 . 84 inch reach
That 8 inches in height and a 10 inch reach advantage
Wilder by KO inside 4 rounds