I meant to post up on this last night but got waylaid.
I was diagnosed 17yrs ago (I was 23), with Type 1, and took up mountain biking as a consequence to try and get fitter / healthier. I haven't looked back since. As has been mentioned countless times above, everyone is metabolically different, so it'd be difficult for anyone but yourself to estimate how long it'll be before you're back on an even keel. For me it was about 3-4 months, but I initially started on a very inflexible insulin regime of one injection per day which was quickly ditched for the more flexible 4-a-day that I've been on ever since. I do seem to recall that the blurred vision cleared up very quickly though.
As Dick Barton mentioned earlier, the best thing to do is keep a positive mental attitude. You're the boss, not your diabetes. The next best thing I can think to say is let your colleagues and mates know that you're ill, how to recognise the symptoms of a hypo and how to treat it. I don't get very good warning signs as my sugar levels drop and I've lost count of the times I've gotten into trouble because of that. From my first ride with Stirling Bike club when Mr Barton spotted what was happening and shoved a Mars bar in my hands, to just a couple of weeks ago on a snowboarding trip when funnily enough, Mrs Barton clocked that I was hypo and needed to get myself sorted.
Those were rare occassions though, both brought on by underestimating the amount of effort I'd be expending and thus overestimating the amount of insulin to take.
When I think about my diabetes, (which honestly isn't that often, it's just there in the background), I'm always remined of the first time I picked up an issue of Diabetes UK's newsletter. It's called 'Balance', and just realising that it's what diabetes control is all about was like a little epiphany. Once you've got your lifestyle and diabetes control in balance it ceases to be such an issue.
I'm fitter and healthier now, than I would ever had been if I hadn't had my diabetes 'wakeup call'. I'm not saying I'm glad I was diagnosed, but I am glad I was diagnosed with something that is perfectly controllable and allows me to lead a normal and happy life.
Sorry for rambling on a bit, but I do wish you all the best.
Beagy xx