I just caught up with homestuck for the first time, and id like to ask: am i correct in assuming that the hore calendars show when the new updates come out? Also, what time do the new updates come out?

Yes, the horse calendars are the days that new updates come out. The comic usually updates in about half an hour. It updates at midnight in some undisclosed European country, but if you’re in the United States it updates in early evening. In the west coast it usually updates around 4 pm I believe and around 7 pm in the east coast.