One way is to look at the row number if even then add 15 if odd add 5

Put this in A2 and copy down column. form cells as HH:MM

=IF(MOD(ROW($A2),2)=0,($A1+TIMEVALUE("0:15")),($A1 +TIMEVALUE("0:05")))

"Josh W" wrote:

I am trying to create a time formula in increments of 15 minutes then 5
minutes then again 15 minutes then 5 minutes etc as follows::
cell A1 08:00
cell A2 08:15
cell A3 08:20
cell A4 08:35
cell A5 08:40
cell A6 08:55
Cell A7 09:10
How do I do this? Thanks, Excel 2003.