When did the disciples experience the gift of the holy spirit?

The Holy Spirit came to the disciples on the Day of Pentecost. The Day of Pentecost was fifty days after Passover. Read Acts chapter 2.

Specifically, at Acts 2:17+18, Peter brings out that this event was actually fulfillment of prophecy from Joel 2:28+29. "'In the last days, God says, I will pour out my Spirit on all people. Your sons and daughters will prophesy, your young men will see visions, your old men will dream dreams. Even on my servants, both men and women, I will pour out my Spirit in those days, and they will prophesy.'