This isn't actually a guide, but I couldn't find any other place to describe some details of the rules that wouldn't fit or be needed in the "Rules" tab.

Timing

First and foremost, the difference between timers. As seen in this gif, the left version of the minesweeper rounds the time UP, but the right one rounds the time DOWN. All official Windows minesweepers round the time UP, so this is the default option. If the version you are using rounds the time DOWN, you must add 1 second to your time to compensate this difference (if you don't, a moderator will do it while verifying your run).

To check which version of the timer do you have, just look if after starting the game it starts instantly at 1 or 0.

The same applies when your minesweeper version shows exact time (the time is rounded UP). If your minesweeper version shows both exact and rounded time, the exact time rounded up is decisive.

Video

In the video, you must show the moment of clicking the button to start a new game AND the end-game screen (if the version of minesweeper you are using has it) AND the whole completed board.

You can submit replay file (MSarbiter, MinesweeperX) or link (minesweeper.online) instead of video recording.

Unofficial versions

You are allowed to use any unofficial version of minesweeper as long as:

• It has the same amount of mines and board size as the official ones.
  Beginner - 9x9 or 8x8 board*, 10 mines
  Intermediate - 16x16 board, 40 mines
  Expert - 16x30 board, 99 mines
• You don't use any options not available in Windows minesweeper or official clones like MSarbiter or MinesweeperX. Specifically, "no guessing mode" on minesweeper.online is NOT allowed.
• You don't use RNG manipulation (in categories that don't allow it) or other options helping to get lucky, low 3BV or generally non-random boards.
• You don't use Google or Windows 8 "Microsoft Minesweeper" (they have separate leaderboards on speedrun.com).
• For browser versions of the game, the full website address must be visible. Specifically, the link to the replay on minsweeper.online must be included.

* Minesweepers had 8x8 beginner board before Windows XP and 9x9 since Windows XP, so both are allowed.