add hours to timetable time cell array

I have a table:

datetime                  cfs 
____________________    ____
{'2026-05-23 09:55'}             271
{'2026-05-23 09:50'}             265

I want to subtract 10 hours from each time, to fix a time zone difference. How can I change all the time values in the cell array 'datetime' by a constant value? also, I want to make sure this will keep the dates consistent, i.e. '2026-05-23 9:00' -10 should then be '2026-05-22 23:00'.

Answer 1

[dpb]

% create table that duplicates illustrated
tT=table({'2026-05-23 09:55';'2026-05-23 09:50'},[271;265], ...
            'VariableNames',{'datetime','cfs'})

tT = 2×2 table
          datetime          cfs
    ____________________    ___

    {'2026-05-23 09:55'}    271
    {'2026-05-23 09:50'}    265

tT.datetime=datetime(tT.datetime,'Format','yyyy-MM-dd HH:mm') % convert to datetime, display to minute precision

tT = 2×2 table
        datetime        cfs
    ________________    ___

    2026-05-23 09:55    271
    2026-05-23 09:50    265

tT.datetime=tT.datetime-hours(10)           % subtract 10 hours

tT = 2×2 table
        datetime        cfs
    ________________    ___

    2026-05-22 23:55    271
    2026-05-22 23:50    265

I'd recomend to rename the datetime variable so it doesn't conflict with the builtin DATETIME() function; while it is allowable, it could lead to some confusion. I'd probably choose

tT=renamevars(tT,'datetime','DateTime')

tT = 2×2 table
        DateTime        cfs
    ________________    ___

    2026-05-22 23:55    271
    2026-05-22 23:50    265

or something similar.

Note that the datetime class keeps time correctly when doing time arithmetic as long as use consistent units such as duration or calendarDuration class variable or function as needed.

As a general rule, you'll be best served by converting date strings to datetime as quickly as feasible; depending upon the way the table was created it might have been possible to have done the conversion when read the data in originally; that part we don't know about since only provided the resultant table containg the cellstr values. Perhaps detectImportOptions might help in that.

Answer 2

[Star Strider]

Try something like this --

A = {{'2026-05-23 09:55'}             271
    {'2026-05-23 09:50'}             265};

T1 = cell2table(A, VariableNames={'Date','cfs'})

T1 = 2×2 table
            Date            cfs
    ____________________    ___

    {'2026-05-23 09:55'}    271
    {'2026-05-23 09:50'}    265

T1.Date = datetime(T1.Date, InputFormat='yyyy-MM-dd HH:mm', ...
                            Format='yyyy-MM-dd HH:mm') - hours(10)

T1 = 2×2 table
          Date          cfs
    ________________    ___

    2026-05-22 23:55    271
    2026-05-22 23:50    265

.

EDIT -- (27 May 2026 at 14:07)

Added Format argument to the datetime call.

EDIT - dpb

Wrapped line so subtraction term is visible without scrolling (with maybe larger font than @Star Strider uses--don't get old <grin>>

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