- During Whodunit Sessions
In all GUMSHOE games, since there is a strong investigative element, the players will often be engaged in long "what is going on" discussions. (as in 15 minutes if you're lucky, hours if you're not!) Use these either opportunistically as they come up, or at the end of each chapter say "this would be a good time for everyone to share their information and their thoughts on what it means with the other experts..." and read while they do that.
- During Breaks
I often go for immersive RP during sessions - no OOC talk, etc. - and I find that to be enhanced with something like 50 minutes on, 10 minutes break every hour, so OOC talk, getting snacks, going to the bathroom, etc. can be done in the breaks. You could then use some of this time to read (at the cost of your own breaks).
- Don't do that, it will suck
However, you shouldn't do this. It's one thing to make up an adventure as you go, it's another to try to use a published adventure without reading ahead - they are NOT constructed for you to be able to do that - that is not a use case adventure designers (especially in GUMSHOE adventures) bother to organize information appropriately for. If you don't know what's coming up across the whole adventure from the beginning, it will end up flowing poorly as you find things you made up on the fly conflicting with facts in later chapters. And you will be distracted from actually listening to your players while you read, and a good GM uses things like whodunit sessions to weave in player ideas to the game. So read the adventure ahead of time, otherwise you are deliberately crippling how good your game is going to be. "Time" is not a valid excuse, you could have read one chapter in the time it took you to post this question. Read a chapter every time you're on the can or something if you truly are time crunched.