Acts 1:3 clearly says Jesus appeared for 40 days after the resurrection. Recently we heard a teacher say it means Pentecost is the only unfulfilled feast & God somehow “owes” us 10 days ( as Pentecost means 50). Then he said that Jesus will appear for 10 days prior to the rapture to fulfill this feast. This we do not agree with, but where does the 50 in Pentecost come from if Jesus only appeared for 40 days?
Like you, I don’t think there’s any Biblical support for this teaching. Most scholars say the Feast of Pentecost was fulfilled by the giving of the Holy Spirit in Acts 2:1-4. In any case I don’t think it’s correct to say the Lord “owes” us 10 days. And He certainly won’t appear 10 days before the rapture. According to 1 Thes. 4:16-17 at the rapture we go up to meet Him in the air. He doesn’t come to Earth at all.
Pentecost has nothing to do with the time the Lord was on Earth following His resurrection. The 50 in Pentecost comes from the fact that it originally came 50 days after the Sabbath that followed Passover.