It depends on many factors. When I worked at a neighbor's, I didn't even get ready, just made sure I had appropriate clothes, brushed hair before I walked over there. I guess making sure I was dressed with brushed hair constitutes getting ready, but, since it was a neighbor's house, it didn't feel like actual "getting ready".
When I've worked at various "yuck" jobs, I was addicted to makeup and had to wear it because I thought it made my flaws less obvious. Sometimes, my eyes had issues with eyeliner and mascara, other times the eyeshadow was irritating. Besides that, everything was fine. Sometimes it took longer because of eye makeup issues.
One thing I never do: take a shower before going to work. I just couldn't bring myself to jump in the shower right after waking up and I never woke up early enough to be gradual about everything. It's the same when I go swimming. Rarely, do I ever just jump into the water. Every once in a while I'll get on a slide first thing, but not that often. I need to approach things gradually, nothing sudden. When I first wake up I want to zone out for a while. When I completely snap out of sleep to full alertness, it takes a while, rarely is it spontaneous.
In general, I dread getting ready for anything. Whenever I have to get ready quickly and figure out what to wear, my mind blanks. I wouldn't mind if I had someone decide all that stuff for me: This is what you will wear today and I have it all set out ahead of time for you.
Another thing, is, so many things make me itch, so if I put on a formal gown or something for a wedding party, did up my hair and makeup with a professional, as soon as everything was done and perfect, I would start itching like mad and would have to smudge everything up
My fave type of attire is very casual and comfortable with nothing that itches, including makeup.
So, to answer the question, it takes me varying amounts of time to get ready, depending on what must be done.