What time zone does the International space station use?

The reality is that the sun rises & sets every 45 minutes; so, the ISS has its OWN time zone. Read here for more info

I would expect it to be Zulu time! Like all aviation.

Back in the days when NASA did not participate in international projects, they used to keep the astronauts on Houston time

International Space Station crews experience a sunset or a sunrise every 45 minutes. New members arrive acclimatised to Kazakhstan time, having departed from the Baikonur Cosmodrome. With so much scope for chronological confusion, it’s no wonder that the ISS needs to be locked to a consistent time. The zone of choice is Coordinated Universal Time (UTC), which is equivalent to GMT.