How old is the plant from clone/seed? It looks quite healthy, if a bit leggy. What light/s do you have on it? Are those pics from 2 weeks ago, or recently? If that's week 2 of flowering then it's doing well, if it's week 4, it's still ok bud growth if a little behind.
It still looks pretty green for a flowering plant, I take it you changed your nutes at the same time as the light cycle? You should be using one with high P & K for flowering, high N for vegging.
It's difficult to say how long it will take to flower without knowing the strain. It looks like an indica dom to me but I'm no expert, that would put flowering time around 8-10 weeks give or take. You really need to play it by ear as the plant grows, theres no hard and fast rule for flowering times but the buds take on a distinctly different appearance as they reach maturity.
Let us know about the age of the plant and the strain if you know it, what light it's under, what nutes you give it and anything else you think might be slightly relevant, the more info you give, the better answers you will get.
P.S. yes the buds will fatten up as flowering progresses.
