One a year, dated, in the same box. That is the whole tradition.
A first-Christmas ornament works as a gift because it is the opening entry in a collection rather than a single object. Date it, keep them together, and in fifteen years the box is a record of a family in a way no photo album that nobody opens manages to be.
Start hereCouples, new homes and new arrivals are the three occasions where this lands hardest. In each case the ornament is doing something a card cannot: it comes back out annually, so the memory gets re-triggered rather than filed.
A memorial ornament is a real category and it is handled badly more often than not. Keep it quiet rather than explicit — an image or a phrase that meant something to them beats a name and dates, which can turn a tree into a headstone.

Production is two to four business days and US delivery three to seven after that, so mid-December is the safe cut-off. Ordering in the first half of December leaves comfortable room, and the first half of December is also when the post is least congested.