So, quick question: my graduated cylinder for my hydrometer is loooooong. way longer than I feel like I need. Is there a reason for this length, or could I saw a few inches off this, thus requiring less beer to steal to take a reading?
I think as long as your hydrometer has room to bob at the necessary readings you should be fine cutting it....
I'd make sure to mark it with the lowest possible gravity you'll ever see and make sure it will still float there.
You don't have to fill it all the way up do you?
Just enough beer to make it float. As long as you can see clearly through the test cylinder no trimming required.
You could put some marbles at the bottom to take up dead space. That would prevent your cylinder from being ruined if you wanted the full length for some other purpose.