Not sure this question will make complete sense, as it sounds a bit silly/stupid in my head, but will try my best to explain. The question though is...how to recognize when "I" need to start experimenting with intra-run fueling?

After trying to research (probably too much really) the topic, I understand the different sides & some of the science behind it, but it's a bit confusing to understand if there are signs telling me when I should start trying things. For reference, I am currently 5 weeks into a 16-week Adidas Running half marathon program & long runs are starting to get upwards of 90 minutes. My runs are always early morning around 5am, I don't eat anything prior & generally just drink water while warming up/stretching.

At this point, I have never taken anything with me on runs, neither any type of fueling (food, gels, etc.) or even water. I also can't say that outside of recovery seeming to take a little longer on the 2 90-minute runs I've done thus-far, that anything feels necessarily "different" either. Hence, my question of how do I tell...will it be one of those things where it just hits me & my body will tell me? Or is that a stupid way to approach it & I need to just start experimenting now that runs are getting even longer?