There are so many ways to shoot a telephone wiring trouble, so here are a few, if not exclusive, suggestions:
I notice that you did not try using a different pair in the 25-pair cable. Use a pair from the yellow group, just as a temporary fix. Pairs in that group, due to the more contrasting colors, are less likely to be punched down incorrectly.
Try inspecting, very carefully, the punch-down of the 25-pair cable at each end, looking for a split or crossed wire. Use a bright light and go at it methodically. There is a one in a million chance that the cable is defective, and a one in 50 chance that you punched down some wire in the wrong place.
When you go off-hook, and there is a delay, it may be that the CO is trying to find the correct Tip for the correct Ring. You may be using the correct Ring with another line's Tip. Some CO equipment will continue to try to provide a dial tone, even if the line is swapped or there is a foreign ground. It may be the cause of the delay.
Once you get the dial tone, does it identify correctly using the CO's ANA feature? Can you call silent battery or establish a call, and if so does it sound clear or is there an unbalanced sound?
Try this: listen to each working line, one at a time, with your test set in "monitor" as you short out the defective line with a screwdriver. Do you hear a click or a crossed dial tone?
Open a all the lines at the source, take a meter and look for a cross between any of the T&R's, testing at the far end (jack).
Open the defective line at the source, and use the meter and see if there is foreign battery or ground at the far end (jack).
Let us know what happens, please.
