Better to do it on Sunday night machan. Because if you do it today, some members will wonder what happened. (Giving some notice for the members before 24 - 48 hrs will be good enough I guess).
Actually Monday night is the best. Because our working EK members are not here on weekends ne. But if you could put a notice in the home page of the current server saying about the transfer, that'll be good again.
And then, hopefully by Wednesday all the DNS records will get updated and hopefully by Thursday people can start browsing again with full speed
