I recall reading in his biography (by Y. Rosenblum. I regret that I have as yet been unable to obtain The Making of a Gadol) that R' Yaakov considered it important to "stay in learning" the first two years after marraige.
It is well known that everything R' Yaakov did or said had its roots in Chazal (See B'Mechitzos Rabbenu for more examples). I would like to propose a possible explanation.
The mishna in Avot provides the following program -at 5 yrs. Mikra (Tenach), at 10 yrs. Mishna, at 15 Gemara. The reader wil see that the amount of time necessary to receive a complete knowledge in any subject is 5 yrs. If at the age of 18 a boy is to be married there remain two more years for which he has to complete his 5 years of Talmud (and after this כל ימיו בעמוד והחזר). And it is from there that R' Yaakov must have reached his conclusion that the first two years after marriage should be devoted to Torah study.
I also recall reading that a certain businessman, who already kept a rigorous learning schedule, wanted to retire and devote all his time to learning. R' Yaakov told him to stay in work saying "After retirement - one starts spending more time with a newspaper and coffee." The learning will not necessarily increase.