Yes, you find more gems in the river. They are, of course, uncut, but you can see the transparent red of quite a few rubies. You find a few clear stones as well, although I'm not certain whether you can identify them as diamonds (that might be something you would know that I don't know you know) as opposed to other clear faceted stones.
You take out the light again, and although the beam is a bit dimmer this time, it works again.
I was not certain whether "if it doesn't work after a couple times" meant "if I can get it to fail eventually by repeatedly trying it" or "if I cannot get it to work again even if I try to use it a few times", but the next roll was a success, and I think that turning it on and off in rapid succession should logically be a single use.
I've hesitated to crunch the numbers on your new growth spell for a couple reasons.
First, there's some uncertainty as to whether you want to develop the light spell because it might be more reliable than the flashlight, or whether you're just going to use the flashlight given that it worked twice in a row.
Second, I'm thinking that your targeted sapling must be a tree of some sort, but I was not certain at first that it was not a bush so I want to be certain I understand what it is you are trying to make grow, and how big it is initially.
Third, I'm not certain whether I should answer your question, but I don't know that I actually can. The baseline suggests a doubling of size/mass in one minute, concurrent with the casting time. The size of the "sapling" is thus significant, since a very small tree will double several times over the first year of its life, but once its trunk is an inch in diameter the percent of growth per year is considerably slower. But then, I don't want to tell you to define the growth in my terms; I just want you to help me translate my terms into your terms.
--M. J. Young