I've done it with the below formula, but it seems a bit long winded:
numberVar tmeTime ;
numberVar Output ;
numberVar x ;
x := x + 1;
tmeTime := tmeTime + (hour({db_field}) * 60) + minute({db_field});
Output := tmeTime \ x;
time(totext(output / 60,0) & ":" & totext(remainder(output,60),0) & ":00");