Checksum and Shifting Expiration Windows
The checksum string is created when the token is processed, so everytime the checksum string is created it has the expiry date based on 'Checksum Lifespan' set in your systems under CiviCRM &gt;&gt; Administer &gt;&gt; System Settings &gt;&gt; MISC.
When validating the checksum is decoded to get the exipry date and checked against now().
Regarding your question

1 -&gt; Yes
2 -&gt; Yes(since the checksum has expiry date)
3 - No