Looks like if you drop one single item on the ground, it will remain there for 5 minutes, which is the right amount of time.
But if you drop more items they will despawn one by one in just ~ 1 minute. I tested this with 18 stacks of different items (two lines of inventory). Even if I drop 18 stacks and one single sword for instance, it will also disappear. The items disappear in the same order they were thrown in. I don't know the minimum amount of items that have to be on the ground in the same place in order for this to take place, I tested it with 18 stacks (thrown from creative).

If any additional information is required, I will be happy to provide it.
Thank you!