Getting hair relaxed for the first time- is it ok to wash before?

Me

I have very thick and wavy Caucasian hair. I’m supposed to get my hair relaxed in 2 days. I have to work Tuesday before my appointment and my shop is very dirty so I need to shower after. Is it ok to wash my hair? It will be about 2 hours before the appointment. If I don’t wash my hair it will definitely have sand/dust from work in it though.