Was Viola back at the covenant long enough during Spring to get any studying done? I assume she was in the regio no more than a few days in real time, but I'm not sure how long it took us to get to Chersonesus. It looks like it's about 800km, which, at 4-5 knots, would take 4-5 days--but I don't think medieval vessels sailed at night. However, this page suggests we're probably looking at over a week (granted, it's for ancient ships, not medieval, but I think 1228 is before the major development in ship design), which would preclude any lab activity other than studying from a book: http://penelope.uchicago.edu/Thayer/E/Journals/TAPA/82/Speed_under_Sail_of_Ancient_Ships*.html I'm not sure if this affects the Aegis casting, since she would probably have started studying something else before realizing she was going to have to cast the ritual.
I think I'll do the roll now anyway, and we can always change things retroactively if need be. I'm assuming a level 40 casting tablet, and, as you noted elsewhere, her total without the die roll is 27. I can't find Covenants right now to look up the casting tablets rules, but her roll was a 7, which should do the trick.
I've subtracted the 8 pawns of Vim vis from the covenant's vis stocks. Do you have any idea when we last updated the stocks? I need to figure that out so that I know how much to add to bring them up to date.