When (by what date?) does a trustee need to distribute a K-1?

[dravenstone]

My son receives a couple of income distributions a year from my grandfathers estate. The estate is managed by a family member with whom I have a poor relationship. I'll spare a ton of editorial here, I just want to file my taxes and I usually just add my kids income distribution in when I file (since he's a minor and it's only like 2K over a year) but the trustee has yet to send a K1. In years past it's taken up until April to get it. Isn't there a time by which he has to distribute it like an employer does for a W2?

thanks.