Yeah, I generally use "Ohayou!" (or the other greetings you mentioned) with my Japanese friends. Sometimes they use "Genki?" (Happy?). But when I was in high school where there were many bilingual Japanese-Americans, we used the casual masculine-sounding expression "Osu!" (pronounced "os") among friends. It's crude for women to use this, but it was a cool thing for us as teenagers.

ohayou is mot nescessary morning greeting, it can be used all day.