A question

First, does anyone know how long it takes Humolog to travel thru the system. For example if you took your blood level now and you tested at 125 and then ate something right away that required four units of insulin how long would it take the humolog to act on that food to ideally bring you back to 125.

Its slightly different for different people. Usually in the range of 2-3 hours (for me its closer to 3)

Humalog is one of the fastest acting insulins so it starts working within 15-30mins which is why many endos will suggest taking it 15mins before you start eating so it is ready to start working when you start eating. It generally peaks between 1-2 hours, but you dont generally get an accurate blood sugar reading til at least 2 hours after you stop eating. Hope that helps.

I agree with Rosemary.  Humalog is pretty similar to Novolog (both very fast-acting), and on the Novolog box it says that the insulin remains active for 3-5 hours after bolus/injection but it peaks about 1-2 hours later.