I think there is a tradeoff in the spring of "early is good" for
quicker takes and more growth vs "early is bad" because its too cold
for the grafts to quickly callous. I do think the trees seem to have
a "better attitude" about grafts done earlier in the season in terms
of putting more growth on them - the grafts done only two weeks later
often seem to be behind their earlier cousins. On the other hand if
you are too early and its too cold to callous then you may lose some.
I have grafted apples too early some years, and I lost a good share of
the grafts. For apples I like temps at least in 50's, for peaches and
apricots I like 70's-80's and for grapes I like 80's-90's. This
spring was very cool and our first 70+ was about ten days ago and I
grafted peaches then; nearly all of them are growing now. I haven't
figured out the best time for persimmons yet, but they are currently
in the peaches category for me due to too many early grafts failing
and which a follow-on attempt later in the spring succeeded.