Nhire, first of all congrats on the offer. Promotions will not come instantly and there is always an element of randomness in such a large outfit, but be assured that with the right projects and network you will be seen and recognized rapidly. The one advantage of coming in at M1 as opposed to say SM is the scope for learning on the role and easily outshining your peers which translates into above average pay rises and better roles (virtuous cycle).