The time on Itch is when the jam is starting. On my end it looks like the livestream is starting 15 minutes before the jam (for PST, livestream starts 8:45 AM and jam starts 9 AM which is the time shown on the Itch page), maybe another host updated the time to be correct in the time? You may want to check again and see if the time is correct now. The theme is revealed at the end of the livestream so a few minutes before the jam.