The day formula stored for this lot is Ascendant plus Venus minus Saturn. It is a plain lot with no other lot inside it, so nothing cancels and nothing doubles: one Ascendant, one fast-ish planet and one very slow one.
Its motion is therefore the Ascendant's, almost exactly. Venus adds about one degree a day and Saturn subtracts about two minutes of arc, so the lot advances one degree every three minutes and fifty nine seconds. A birth time good to the minute gives a placement good to a degree; a birth time given to the nearest quarter hour does not fix the degree, though it will usually fix the sign.
The arithmetic is the least of the difficulties with this lot, and this page's own description already records the reason: several incompatible formulae for a lot of marriage circulate, differing in which planets are used and in whether the terms reverse by sect. The formula above is the one this atlas stores. Any comparison of two marriage lots from two sources should begin by establishing that they are the same construction, because two lots bearing the same name and built from different planets are not two opinions about one point, they are two different points.
That is a general caution about the medieval expansion of the doctrine rather than about this lot alone. Bonatti transmits a very large number of lots, and the further from the Hermetic core a lot sits, the less agreement there is about how to build it.