I don't know if anyone else has any better answer to this, but it honestly seems like c-cex have messed up the time configuration on their API.

Looking at their API documentation, it seems they use a new time format for every API call, which is not good at all.

As for a fix for this, if you know their API is offset by X days you could just subtract that from the timestamp c-cex returns. It's really not an optimal solution, but their API seems really bad.