Converting time from text to hours and minutes in Excel
With data in A1, in B1 enter:
=TIMEVALUE("00:" & SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1,"m",""),"s","")," ",":"))
and apply the proper format:
EDIT#1:
If you have only seconds in a cell like:
28s
Then I would use:
=--SUBSTITUTE(A1,"s","")/86400