Remove pedals, wheels, saddle and seatpost.
Slacken handlebar stem bolts

I have a 57cm road bike, with a 130mm stem fitted.
To fit my bike, I remove the seat post (with saddle), wheels (!), rear dérailleur and the handlebars from the stem (leaving the stem attached to the fork tube).
To leave the stem on, I rotate the forks 90 degrees so the stem points "up", and there is plenty of clearance.
I could possibly risk leaving the rear dérailleur attached, but there is only about 3mm of clearance between the rear most part of the dérailleur and the side of the box.
With a slightly "shorter" bike, as your 52cm frame would be this would probably not be required.
Even if it is required, the RD is held on with one bolt anyway, and doesn't need any re-alignment (in my case anyway)

If you have pannier racks, mudguards etc fitted then your mileage may vary...

I had a 58cm frame, I had to take of Pedals, Seat post and handle bars,

I have a 54cm TT bike, and I have to remove the handle bars and fold them down onto the bike. I suspect with a mountain bike, you would just need to turn the bars rouns flat to get it in the box.

Check the manufacturers website, as it should tell you. It is heavy, I think about 7.2 kg, but don't quote me.

9.5 kg

yep

Yes, it would fit comfortably.

no way

It'll easily fit a 56cm carbon frame road bike no problem. I got my 55cm alu road bike in there, and had plenty of space left for helmet & stuff etc..

I have a 2009 Scott Addict R3 (54) with integrated seatpost and the bike fits in easily. It is necessary to remove the seatpost cap and saddle. Worth noting the seatpost is cut to fit to my 5'9 height and i have a compact chainset. There is however about 5-6 cm space between the top of the seat post and the top of the Bikebox. If you have a longer seatpost or a standard chainset you could always remove the chainset to fit the bike in.