leggots advice is pretty spot on..
Sugar levles can go very high indeed, home glucose meters tend to give a 'high' reading once the BG's reach 33mmol/l partly because above this level they can become very inadquate.. and partly because if you hit these types of BG's you really need seek medical advice..
As to the insulin duration, 2 hours is about the peak, at this point the body as used about 60% of what has been injected, the remain 40% tails of over the next 2-3 hours.. So if you given another correction Jab keep this in mind when calculating his next jab, this will help prevent 'stacking' where you get a sudden drop of BG's caused by 'stacked insulin..
This is important to remember when his levels are getting around the 12mmol/l mark, the higher the BG the resistant to insulin it can be so can need a little more, but the problem is that if you've got stacked insulin, and the resistence falls off, the BG plummets quickly..
A couple of things to watch for that might identify he's struggling and requires medical attention, if he becomes pale, or unresponsive (hard I know at night when he should be asleep) if he complains of stomach pains, feel sick or is sick, his breathing becomes shallow, rapid pulse, is breath smells best discribed as smelling sweet, pear drops, damp straw sort of smell these are the different signs that he may be going into DKA, he could have several or only one... But any concern or doubts, either call the doctor, take him to A&E or get the paramedics out to you..
I hope all goes well, I would give his diabetic team a bell first thing in the morning as he may need more close monitoring, as this could be a sign that his honeymoon period is drawing to an end, and might have to start looking at how you may deal with introducing a different/new regime..
Take care
Jo