Is it ok to finish the Game on a cliffhanger? 

It would be kind of a "Chapter One ending", but still leave some loose ends... 

The ending is the the part your player is going to remember the most, it would be more impactful if it ties up all of the loose ends. I think if you intend to use this game as "Chapter 1" to a larger game, then you could insert more into Version 2's "Chapter 1" to lead more into the narrative you'll have included by then, if that makes sense.

It's a good point. 

I just didn't wanna rush things up just to include the ending... Chapter one would have a good amount of questions answered, and fits perfectly in 1 hour of Gameplay. 

I just wanted to make sure it's ok according to the rules =)

All you need is an hour of gameplay. Focus on making that hour awesome first, THEN if you have time worry about an ending