Pivot Table

I have a dataset consisting of Date and Time data (in separate columns - one has date i.e. 13/06/2024, and the other has time 11:30:00), along with measurement data. The data frequency is every 15 seconds (11:30:00, 11:30:15, 11:30:30, 11:30:45, etc). I wanted to turn the dataset into 1-minute average instead - so averaging 4 15-second rows into 1 minute (11:30:00, 11:31:00, 11:32:00, etc). Previously I had used the offset function (=AVERAGE(OFFSET($A$2,(ROW()-ROW($C$2))*4,,4,))), but it is manual, takes a lot of time, and doesn't work properly if there are irregular data (i.e. if there are only 3 15-second rows for the minute instead of 4 due to measurement error). So I turned to Pivot Table to try to make it work better. However, when I used Pivot Table, the summarise function works but the format is quite weird: instead of having the proper minutely data (11:30:00, 11:31:00, etc), it listed the data in the hours, followed buy the minutes (e.g. the rows are sorted by hours (11, 12, 13, etc.), and then the minutes are shown separately (30, 31, 32, 33, etc.). Is there a way for it to display the data as 11:30:00, 11:31:00, 11:32:00,... in continuous sequence instead of grouping the rows?