| I'll do corrections at the 2 hour mark. I base my decision on a table that gives numbers of how much of the bolus shot should have been used up.
This is for Novolog, Humalog, and other 4 hour fast acting insulins:
Time used up% -- remaining%
.5 hr 10% -- 90%
1 hr 30% -- 70%
1.5 hr 50% -- 50%
2 hr 70% -- 30%
2.5 hr 80% -- 20%
3 hr 90% -- 10%
3.5 hr 95% -- 5%
So at the 2 hour mark, I can check my blood sugar, and let's say I get a reading of 190 mg/dl. My mealtime bolus 2 hours ago was 6u, so I'd estimate that I have 1.8u bolus units remaining. My correction factor is right around 35 mg/dl, although it varies some due to time of day. 35 * 1.8 = 63 mg/dl drop still to come, which would put me at about 130 mg/dl.
Based upon that, I'd likely give myself 1.5 to 2 units of correction bolus, although as always it's dependent on what I think I'll be doing over the next few hours. | 
