Changing medium NRT to 24 hours for Priority Support

Why is this change being made?

This is being made as per:

• this epic
• this dicusssion issue
• this implementation issue

Relates to gitlab-com/support/support-team-meta#3556 (closed) Relates to https://gitlab.com/gitlab-com/support/support-ops/support-ops-project/-/issues/520

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)