| Hi Jill-O...it was helpful for me years ago to pull the graph out of the packaging...the graph that shows the "work schedule" so to speak of the two insulins.
The Lantus takes about 4 hours to get up to 100% speed...but it will overlap some already in your system, so that is not noticed by many people.
Humalog will kick in pretty strong in about 30 minutes to one hour...give or take. I have gone a low if I take it too early before a meal. I try to take slightly before eating or immediately after.
The two are completely independent of each other...but if taking too much of either one, you will definitely go low (reverse is true)...
If you are having trouble with glucose numbers, then double check basals (Lantus) before trying to fix bolus (Humalog)...I struggled for years trying to do this on my own...endo wasn't much help because you really have to figure it out on your own. I just wish I had been given more info on the two insulins when first prescribed...other than short acting and long acting.
I really like the two...after a few years of "getting to know them"! Your meals are totally flexible now.  | 
