The changes mean branches, including many in the West Midlands, will operate from 9.30am to 3pm on weekdays, instead of until 4.30pm.
The bank said branch staff will still be available for pre-booked face-to-face appointments between 3pm and 5pm, if customers need support that cannot be provided through alternative channels or earlier in the day.
The shake-up will also see 316 branches move from being open from 9.30am to 4pm on Saturdays to operating a half-day service, closing at 12.30pm.
Those affected by the reduced hours on Saturdays include: Dudley, Kidderminster, Stafford, Stourbridge, Sutton Coldfield, Tamworth, Walsall, West Bromwich and Wolverhampton.
In Shropshire the Oswestry, Telford and Shrewsbury branches will see Saturday opening hours cut.
Face-to-face appointments can still be made at these branches until 4pm.
The bank said the number of customers using its branches fell by a third (33 per cent) over the two years before the coronavirus pandemic, and a further 50 per cent in 2020 and 12 per cent in 2021.
Santander bosses have confirmed the changes will take place from July 18 and there will be no compulsory redundancies or a reduction of employee working hours as a result.
The bank also plans to beef up its telephone support for customers and said branch staff will be trained to help on the phone alongside their current face-to-face roles.
Meanwhile, 76 branches will retain their current half-day opening hours on a Saturday, and 58 sites will remain closed on a Saturday.
There will be no branch closures as part of the changes, Santander said, adding that all of its 450 sites will remain open every weekday.
There will be also be no change in the number of branches open on a Saturday, with 87 per cent of sites operating from 9.30am to 12.30pm.
The bank said the changes reflect a thorough review of when customers use its branches.
Richard Owen, head of branches at Santander, said: "These changes will enable us to maintain our existing branch network while providing significant additional capacity to help customers who want to talk to us by phone.
"We have seen a continuing reduction in branch usage over several years, both before and since the peak of the pandemic, with many customers preferring to transact digitally or contact us by phone.
"We want to make sure we have the right mix of channels to help our customers however they choose to bank with us."
Santander said it will be writing to regular branch customers to explain the new opening hours and to offer support.
Bank branch and ATM closures in recent years have sparked concern about people being easily able to access their money. The Government has said it will legislate to protect the future of cash.
Several industry initiatives have been taking place, such as cashback in shops, and shared "banking hubs".
Santander said it remains actively committed to the wider access to cash movement, with representation on several industry working groups and participation in the Cash Action Group's shared hub initiative.
A handful of branches situated in shopping centres will be excluded from the changes, including those in Gateshead, Sheffield and Basingstoke.