I wish I could post a big batch of birthday cards in January and they arrive on the right days throughout the year. Would mean much less rushing and forgetting.

I get some cards for my birthday in the days preceding it with 'do not open until [date]' written on the back, presumably by wise people posting early to mitigate Royal Mail risk. Could you extrapolate this approach across the whole year, posting the lot in Jan, with suitable 'do not open' dates?