Two years six months is also a reasonable time as some companies have salary discussions only once per year.First time around, you might have only been at the company for a short time, after your first full year you might not be able to, want to go for a salary raise or you might not get it, but if you don't get it the second time, it's a sign that is hard to ignore

This is, though, with an asterisk that you made a reasonable effort to get your raise.

If you didn't, for example you had too much going on in your personal life, and therefore you couldn't put in the quality hours, it might make sense to just be happy with what they give you as in other places you might not be able to tend to your personal stuff as well as in your current company.