Rav Yosef quotes the posek: V'nason ha ish hashocheiv ima l'avi hanaara etc." as proof that the father is not zocheh the money until it's given over to him. It seems as if the limud is the past tense of "nosan" given over.
It was pointed out in our shiur, however, that v'nosan is not really past tense at all. I thought about this and it seems to me that the vov hahipuch in a case like this is never past tense. If there's a verb with vov that has a shva under it then the verb will be tziyvuy-commandment such as: "Ve'yaasu bnei Yisrael at haPesach bmoado." Bnei Yisrael shall make the korban pesach future (yaasu to tzevuy) or "V'asu li mikdash" they will make me a mikdash (past asu- as a tzevooy or future if they make me a mikdash I'll dwell amongst them).
Even conditional - v'achalti chatat hayom-Aharon said: "Had I eaten the chatat today would it have been pleasing in Hash-m's eyes?" It never means past tense. To make a verb into past in Tanach Hebrew there would have to be a patach under the vov. Vayaas and he did. Vay'daber and he spoke. Vayechoolo and they were completed. So what kind of limud is Rav Yosef making here?
In almost all of the payments which one is required to make in the Torah the pure future tense is used. (See Parshas Mispatim: Shivto Yiten , Shalem Yeshalem , Shenayim Yeshalem , Yeshalem Shenayim, Kesef Yishkol etc.) The Gemara here is learning a Halachah from the fact that the Torah does not write "Yiten," but rather "v'Nasan."
It is a common misconception that the Vav ha'Hipuch reverses the tense of the verb such that it is exactly as though the opposite tense was used. However, as a rule, there are no pure synonyms in Lashon Kodesh, and this is no exception.
The difference between past tense and future with a Vav ha'Hipuch is explained in Rashi Bereishis 4:1 (DH veha'Adam Yada es Chavah Ishto). Rashi places this event before the previously mentioned events in the Torah by virtue of the fact that it does not say " va Yeda." From this we see that Yada (past tense) and va'Yeda (also past tense) do not share the same meaning.
The difference is the point of reference. When we say "va'Yomer Moshe," we translate it as "Moshe said," since from our point of reference, as listeners to a story about what once occurred, it is a story of the past; Moshe spoke two thousand years ago. However from the point of reference of the narrative it is not past tense; the sequence of events is happening in the order that it is written. That is also the meaning of "va'Yeda."
However, when the Torah says "veha'Adam Yada ," it means that it is referring to something of the past even from the perspective of the narration. That is, it occurred before the events recorded before that in the Torah. Therefore Rashi deduces from the use of the word "Yada" that the story about to be related preceded the previous events; it was past tense even from the point of view of the narrative. (This idea is explained and proved at length -- although in different terms -- by the Kesav v'Kabalah on the above verse, Bereishis 5:1, and on the verse "v'Yakov Nasan," Bereishis 25:34.)
There is a similar difference in a verb of the future tense like "Yiten," which is written without a Vav ha'Hipuch (future in terms of the narrative and in terms of the listener) and the same verb when it is written with a Vav ha'Hipuch, like "ve'Nasan" (future in terms of the narrative, but with an element of past from the point of reference of the listener). The latter reads as if said "And it will come to pass that he will have given." From this the Gemara learns that the money is the father's only after it has been actually given to him.