waldo, that's not exactly correct. Brokerages generally "give" 5 days for a margin call, but technically the call is DUE IMMEDIATELY. That's because if the equity level is approaching the point of going negative (in extreme cases) they can sell you out at any time at their descretion even if it's just the first day of the call.
***Brokerages call sell you out at any time if they deem it appropriate to protect their own risk exposure for the margin loan that they have extended to you.***