In case anyone else is wondering about this, joebedford's advice was sound, if obvious - it depends on the custodian!

Vanguard, for example, wants to receive the paperwork by their close of business Monday - though there is something on their web site about doing an on-line application and getting electronic confirmation of some kind, again before COB Monday. On the other hand, T. Rowe Price (in nearby Baltimore) is pretty obliging if you live around here. Their investor centers will be staffed and ready to take your money Saturday, Sunday, and Monday until 7 PM. (Sort of like the Post Office does in many large cities, having clerks in the lobby, and often at curbside, postmarking tax returns right up until 11:59 PM April 14th...)

And Phil, your advice was good as well, and it occurred to me shortly after I posted: establish the IRA at local bank, and subsequently transfer to another custodian if desired. Now I just have to get Number 1 Son to go along with the program.

Thanks, all - Lorenzo