A holiday timer seems like a good idea in theory, though in practice I see an opportunity for abuse unless this game mechanic is thoroughly, thoroughly planned out. Example: You're about to be attacked, and suddenly decide to take a vacation. In the mean time, your allies move in to reinforce you with troops and supplies. Even if you pause for a holiday, this doesn't stop other strategus players from doing shit. And just making Christmas a day for no strategus action would be totally unfair--there are other fucking people, who celebrate other fucking holidays on this planet than you. What holiday's count, then? Which one's "aren't important enough"? Who gets fucked, and who doesn't, in this system?
The absolute best solution to the issue involves not having to create any sort of game mechanic; the players should simply take it upon themselves to be respectful and knowledgeable of each others major secular and religious celebrations. Of course, this doesn't always work--as the recent Druzhina attack demonstrate.
However I might point out that OP's point is that "strategus isn't my life". Oh no, you lost some video game territory and equipment because you were attacked, and poor little you just had to place your fucking family first. Boo hoo. Your lost troops and equipment should seem inconsequential when seen in light of the happiness you experience when you are with your friends and family over the holidays. The offending attacker, whether acting from ignorance or victory-lust, will have lost more in prestige and respect than you could have possibly lost in in-game assets.