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.
Salary discussions can happen at any time, though. Restricting it to once per year is just delaying tactic. If you resign and they want or need you, all of sudden everything is possible
Vast majority of large, publicly traded companies (at least in the US) only do pay determination (and associated raises) once per year. Promotions can definitely happen whenever but there may be a cycle associated with that as well.
You truly believe that such rules are written in stone? There's always exceptions if a need arise. Budgets of whole countries can be changed mid year but salary of some employee can't? :)
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.