[sumo] Time for the Makunouchi shikiri-ken?

[Jezz]

Murray Johnson on the NHK broadcast has now said twice that the
Makunouchi shikiri-ken is about 5 minutes....  I always thought it was
meant to be four minutes (but in reality, is a certain number of
visits to the 'salt corner' - I think four), with the last visit being
when one of the shimpan (the 'time-keeper') raises his hand - and the
rikishi are handed a towel....

So my question is, is the shikiri-ken about 5 minutes as Murray
Johnson said, or 4 minutes, as I was led to believe....  or both.
I.e. officially it is four minutes, but inreality it is closer to 5?

Thank you in advance :-)

Jejima