Windows (.exe) IGT: This is based on the game's code de-compiled by Lassebq. One detail to note is the displayed time is rounded from the precise IGT, so the seconds you get at the end might not agree with the official time. Here is the process of converting the end-game code into IGT, with ohon's 2:02 as an example:

1. For code like "a####xxxx.x0b8", make note of xxxx.x (ex. "a9-15a167.40b8" -> "167.4")
2. Subtract 86 and divide by 33. (ex. "167.4" -> 2.467). This is the fractional number of seconds, precise to the frame count.
3. Append this to the number of minutes (ex. 2 m 2 s 467 ms)
4. Because of a rounding error, a minute on the in-game timer is 59.5s, so 0.5s is subtracted for each elapsed minute (ex. 2m 1s 467ms). This is the precise IGT.

Manual timing: Here are some facts about the Windows version IGT, in case a video does not show the end-game code:

• IGT seems to end on the 5th frame of the screen transition, when the boarders of the diamonds touch. You can count the frames after the timer updates to the previous whole second. The frame before has a gap between the diamonds.
• The background cloud pixels give you a visual reference for elapsed frames, since they move 1 pixel per frame. This should let you deduce the IGT with decent precision. Worst-case, you can use some external stop-watch to get the time to the nearest 0.2s or so.

Flash IGT There is no in-game timer, and the game seems to run closer to 60fps. Until someone does some tests on this version (My computer doesn't run Flash), we will assume the game ends 0.2 seconds before the timer shows during the final screen transition.