I want to create open wifi in my office with web based authentication (captive portal) for every users.
One password for all with time period.
Is there any Mikrotik product like RB750 or RB951 with this feature
Yes it is. Just look at hotspot at mikrotik wiki page
I have used Mikrotik hotspot, there we have to configure username/password for each user
my requirement is one common password for all users