Hey Roxy
I'm newly diagnosed and I've started swimming as well on a semi-regular basis.
A little tip I can give is - your meal before swimming sounds awfully light? I usually go after breakfast. I know, being a student and it being revision time is amazing for having time for that kind of thing when you want to, so it might be hard if you're on a working schedule. Anyway. I usually go about 2-3 hours after a big breakfast (often including oats and some kind of fruit), so that my lunch should be within 1-1½ hour after being done with my swim. Reason I do this is mainly that meals make soooo tired that I need exercise to give me energy, but I've found that eating lunch after a good 40-60 minute swim doesn't do so.
I then usually follow up with a carrot or an apple after the actual swim. I don't really know if I should do this. But it makes me feel quite good.
Anyway! What I wanted to say is, that maybe you shouldn't necessarily be swimming for the BG levels, but for the other benefits? I've been doing so for six months - first once a week, then twice, aiming for three come August. And I've not only noticed weightloss (11lbs!), but also that my back is straighter and my stamina has increased etc. Swimming's really great for that.
About the BG levels, though, if you do find out, please let me know
I'm waiting for a measuring device to arrive via mail, so I'm going to start testing after my swims for a few weeks. I can keep you updated if you want?