How come you grew them vegetatively for ten weeks? How big were they at ten weeks? There's no point growing the plants for a long time when they are being flowered with only 250 watts. I use a 250w myself and I only veg for a couple of weeks, unless I've started from seed then it takes a while longer.
The light from a 250w lamp cannot penetrate much foliage so the most efficient way to grow with 250w (in my opinion) is to have lots of smaller plants left unpruned so they only have one cola (sea of green or screen of green method) as opposed to fewer but larger plants. This method is quicker as the vegetative period is very short, so your clones are in and out of flowering quickly. The set up I have now is- A small cabinet which is lit with 110 watts of fluorescent light, this is the mother and clone chamber so I've got a constant supply of clones; and there's the flowering chamber which is lit with a 250w HPS. This set up will allow me to harvest every 56 days. The clones are taken from the mothers, rooted and veged until the others in the flowering chamber are ready to pull. Then the new clones go in and so on, and so on; a constant cycle.