1) a company of ~50 people doesn't sound like a start up to me, and calling themselves one just reeks of opportunism at the cost of the employees
2) there's plenty of work in Vancouver
3) as others have commented, constant crunch is neither healthy nor productive
4) talk it over with HR, if they continues to seem unreasonable, go somewhere else. Your mention of two others that came before you but left after a short time raises a red flag