I'm semi-new to gardening myself.
Those are Nice pictures! & good questions. I am growing the same kind of cucumber as you are this year. It would have been a useful fact had I recorded exactly when they stopped growing upwards and began vining. (But you are right, there are a lot of factors that influence that.)
For what it is worth, my first thought was that yours looked good.
I remember the first time I ever grew cucumbers I got scared when they toppled over!
Then they began crawling on the ground with vines and everything was illuminated. I thought it was funny I thought the cucumbers falling over was a bad thing at first, hah! It really did feel sudden when they began vining, it didn't feel like it was going to happen, like ever. Until it really did. Then once they get going they go!
I really like your structure /the trellis/ what you have given the cucumbers to grow up (from what I can see)! I'd like to see how it looks when they all start vining (but no pressure!
), I wish you all the luck of the earth!
(P.S. I'm no expert of course / don't take this as your final word, but the leaves of the same type of cucumber I have in my garden were smaller than yours when they started vining: I think yours looks really nice and should start vining soon, especially if they've been in for a month & it's been cooler. I can tell they aren't getting burnt by too much sun which is one of the main obstacles where I live, ultra sun valley. Last year the sun in May killed my lemon cucumber! No contest. This year I started early to avoid that if at all possible!
Cucumber plants are so cute/cool to me... they seem like they'd never become vining monsters like do from just the little bush of a plant they are for so long in the beginning. It is awesome.
I have more experience with armenian cucumbers (which is actually a member of the muskmelon but used like a cucumber), but this year I am growing the cucumber in your picture, "bonnie burpless hybrid", a lemon cucumber, & a Japanese long cucumber.
In addition to 3 Armenian cucumber plants grown at my MIL for us, we are going to have a cucumberpalooza if we can help it. I look forward to making tomato-cucumber salad with the 4 different kinds of cucumbers and a rainbow load of different kinds of tomatoes. But I digress!
Anyway, I hope a real cucumberologist can come give you a definitive answer soon. It was good "talking" to you!