Like a lot of startups - deadlines are frequent and schedules are aggressive. This leads to hours becoming long when a difficult milestone approaches. And because management is purposefully selective and thorough during the hiring process, help has typically always arrived a bit later than when it was needed. Note though that this was as of Q3 2015.
Additionally, the company is growing rapidly, which opens the door to the month-to-month work experience changing dramatically. Over the two years I've been here, R&D has more than quadrupled in size. Work structures and facilities have been slow in catching up with the expanded population leading to some disorganization, redundant efforts, etc. I am hoping the company's organizational structure becomes better at adapting to its rapidly changing size going forward.