Hello, here is some information about your situation you may be able to use to determine the time frame:
You are not allowed to play on Diablo 2 Battle.net servers with an active VPN, while behind a proxy and/or if you are using a business class internet service provider. All three will automatically restrict your access to Battle.net for exactly two weeks from the last occurrence. While a restriction is in effect, attempting to connect without any of the three being true will not reset the duration. Blizzard will not remove the restriction for any reason.
Be sure to disable the VPN before playing Diablo 2 on Battle.net and/or don’t try to play at work and you’ll be fine.
Brief history on why this is the case: Hackers, item farming bot runners and illegal item selling advertisement chat spam bots were using a combination of business class ISP’s, VPN’s and proxy setups to engage in their game ruining shenanigans/money making schemes, which was ruining the gameplay for everyone. Due to the games archaic game code and net code, restriction of Battle.net access for usage of VPN, proxy and business class ISPs was the best solution they found to keep the servers stable.