Sorry, Santiago, I have to disagree. By convention in the RAF, times are to the nearest 5 mins; therefore a 4 min flight in the auth sheets would be entered as 5 mins. As would any time less than five mins, including 2 m 25s! Whether you choose to enter zero mins in your log book or not, I guess is up to the Sqn policy; all Sqns I've been on insist that auth sheets and logbooks match.
Unless, of course, the roolz have changed in the last couple of years???