The problem with any answer given here is that it could very easily change. When you ask the question of a recuiter they will generally give you an answer based on what is happening at the time the question is asked, i.e. at the current time, upgrade at Emirates is three years ( that is for people hired three years ago ), it will not be the same for someone hired today.
When I was hired by a major in the States they told me five years, because that is what is was at the moment. It is now 16 years later and I am no closer to a command at that airline than I was then
What you need to do is get the profile of all pilots on the seniority list and of the airline's current expansion plans. Based on retirement dates and growth of the airline you could calculate time to upgrade. Of course that is all based on nothing changing between the time you make the calculation and the time in the future that you predict you will upgrade. It never works that way because we work in a rapidly changing environment.
The bottom line is that it is best to get on with either a rapidly expanding, profitable airline or one with a large number of retiring pilots in the near future.
Typhoonpilot