I swear there used to be a button on the right-hand side in an ebay listing where you could just click "Snipe This" and open up your Snipe input form. I can no longer find this button. Am I spacing out and just not seeing it or did I hallucinate that that ever existed at all?

The "Snipe these" button is available when you install Firefox add-on on your Firefox browser:
https://addons.mozilla.org/en-US/firefox/addon/5571/

or Google Chrome extension on Google browser:
https://chrome.google.com/extensions/detail/fmebanjjkaohcmifehogijfgcoieefnp