Can't figure out the last success (<65536)

[Gwido]

Is it just a matter of play time ? :(
The in game "clock" made a rollback at least 6 times since I start the game.

The full game is cleared, I got the 4.5 secrets, and it's very disappointing not having this last one success. :)

[Amicable Animal]

It's an achievement all about time, yes! It is a speed running achievement: can you reach the credits before the 'clock' shows the value pictured? (It's relatively generous, but very unlikely you'll do it on your first run) You will need to start a new save slot for it from the main menu!

[Gwido]

Ok. Thanks. :)

[Demimind]

I couldn't make out any clock. I've gotten all but 2 achievements, one of them is the speed run. But does the number 65536 apply to the number of seconds? That's about 18 hours and I have about 10 hours of game time logged. Or is the number arbitrary?

On another subject, what do the two 2x2 symbol groups mean on the pause menu? I notice they change every time a previously visted room is clicked on. Does it have anything to do with the combination lock towards the end? I never figured out myself how to do it and needed a video guide.

[Amicable Animal]

The two things you are talking about are actually linked!

Look out near the centre of the world, near the battery hub, and you'll find the clock. The number isn't arbitrary, but is... well, very difficult to translate. The game has its own number system. You don't need to translate it to figure out the achievement, just finish before the value shown.

The symbol groups on the pause menu give you coordinates for the room you are in, and can help translate that number system. The combination lock isn't related, and is probably easier than you think, once you spot it. Take a look near that room, but at a different level...