I attached a piece of raw zucchini to a slip sinker / fishing weight. So far the fish are curious, but not eating it. My question is - how long do I leave it in the tank for? wondering if they will take to it once it softens? any tips or insight as to how to feed their fish vegetables or fruit?

one time, i am eating boiled corn in cob while watching the fishes.... out of
curiosity, i throw in a mouthful gain inside and to my surprise, the pangs and
oscars compete for it.... from there on, i used to throw-in any food i have
( orange, pineapple, banana, crushed cucumber) except those oily foods.

I have tried to put cucumber in my tank and no one cared. It was more for the pleco but I think he is too old and set in his ways to try something new.

It sometimes takes some time for the plecos to get used to the new food.
On the other hand they may never eat it, although all of my plecos love it.
I tried potato, spinach, banana, cucumber and they don't eat those...
If tanktemp is above 76o the zuchinni will soften and fall apart within a day, so i suggest to remove it before that.
The softened part can be a major pain for your canisters, for the slimy goo will clog your filter
They will eat the hard stuff anyways.
I put in a quarter of a zuchinni and it will be gone within 12 hours.

Some people parboil the zuchinni for a minute before feeding it, but i just scrub and rince it well to get of any possible chemicals.

As for the weight you use make sure there's NO lead in those weights, for lead is extremely poisonous for plecos and can very easily kill them.

Place the food close to their cave and if they eat algae wafers you can try sticking some into the zuchinni, to see if they eat it then.