Are you sure that's 2 1/2 weeks and not 1 1/2? From my experience, and granted it is minimal, I'd say they should be almost triple that size by now. What are they planted in? What light and how much are you using? What's your watering schedule? Give us some details and we can give you a better answer Welcome to the forum man! You've come across a plethora of information, and a ton of great people willing to help.
What solar system is your planet in? Lol its small, but looks ok I guess. Why is it so far down in that cup? Kinda hard for light to penetrate the plastic yo.