My concern however is on the deadline given for all customers to withdraw their money. For a casino that has been operating since 2014. I believe it's a short time frame. At least give your customers a chance. Maybe 2-3 months.
I believe that if all people who have money on the site are people who use the site every day they must have seen this announcement and have plenty of time to withdraw their money then in my opinion this time the OP has given is enough and fair time for people to withdraw their money, of course assuming the withdrawals are processed quickly will allow everyone to withdraw their money from the site
Aside from the announcement on this thread as well as on the website, I think betBTC also inform their players through email so all players aware about it and if they have some balance left on the site then they can withdraw it as soon as possible. If betBTC has done it, it is more than enough and perhaps they can re send the email few days before they shut the site down.