What I have seen is that it’s around one year. Sometimes Masses will have both deacons and priests ordained at the same Mass, but nobody who is ordained both at the same time. In our diocese, ordinations typically occur in June.
I can only speak for what happens in my diocese. I am not sure what, if any, standards there are and how they are applied place to place.
According to canon 1031§1, a priest must be ordained as a deacon for a minimum of 6 months before they are ordained to the priesthood. This is similar to the requirement of canon 1035§2 that requires a minimum of 6 months between institution as an acolyte and ordination to the diaconate.
In general there is one year between each of these phases because they are generally done according to the accademic calendar. Since this is ecclesiastical law, I suspect the time periods could be dispensed by the proper authority.
As Usige points out, Canon Law requires a 6 months minimum period but if anything, a longer period is normal although dispensations are possible. I don’t think that there is any provision for ordaining a man a deacon and priest in the same ceremony (as opposed to ordaining separate people deacon(s) and priest(s)). Even the Anglican Ordinariate priests were ordained separately to the diaconate and priesthood - even if only a few days apart in some cases.
Canon law is clear a priest needs to be at least 6 months a deacon before they can be ordained to the priesthood. However it is to the discretion of the bishop to accept a deacon into the presbyterate. So technically it could take years too.