I don’t normally eat on the trainer but eat something 20 mins before I start.
Today was going to be a hard threshold session so did make a bottle of homebrew carbs. After I finished it with 30mins to go it got me thinking should I have done more bottles? If I had drunk anything taken just before the last block would it get used? Approximately how long does something simple take to be usable?
I was swinging some slight cramp so it wasn’t enough salts, or something that’s for sure!
About 10 minutes or so, IIRC 
Over worked muscles . I doubt salt would help unless it’s a real long session.
Sweet, should have made a bit more then!
Side note, username from up in the Lakes? Bet it’s lush in the snow right now.
Overworked, or left shoe not right fit, is a good point. I was trying hard!
Yeah. I lived up here for most of the 1990s and then again from 2014 to date and not planning on moving far. It’s rather lovely. I’m north of the park, so I avoid the crowds. 
There can be signaling (resulting in energy boost) as soon as something sweet hits your mouth. Studies have shown positive impact from carbs with just a mouth rinse without even ingesting them. Not sure it would have helped your cramping or not. For me, pickle juice is my go-to as a very temporary solution for managing cramps. Similar studies show that pickle juice, hot sauce, mustard, etc. can have an immediate impact on cramps once it hits your mouth. So much of this stuff is neurological, basically tells the body things are going to be OK because help is coming from the food/drink you just put in your mouth.
As far as carbs/fueling during a workout, I try to fuel pretty hard from beginning to end for any hard session. You aren’t likely going to end up with a calorie surplus regardless of what you eat/drink, so it’s really just trying to minimize the deficit and trying to stay ahead of recovery coming off the bike. And there are some advantages to ingesting carbs (especially simple carbs) during an exercise window vs. other times of the day.