It depends! For me it took me 1 hours more or less... It depends on how you play! Anyway, there's a wat to see how many pantsu you have by reading a text file in the game files! I'm not sure where is it, but is there somewhere xD

Check the following directory:
%USERPROFILE%\AppData\Local\Montaro\User Data\Default\Local Storage\

(%USERPROFILE% is typically "C:\Users\USER")

In that directory, I found a file named "chrome-extension_pionmdlpdbkonlgpimjbaminkcbdgjnm_0.localstorage". I opened that in Notepad++, copied the contents and pasted into a new file (this got rid of the "NUL" characters). Press "ctrl+f" and search for the string "c o l l e c t _ p a n z". You'll find something that looks like the following:

c o l l e c t _ p a n z 6 4 7

I'm assuming that means that I've collected 647 pantsu so far.

I just pasted the comment I found in a discussion! Hope it'll be helpful! :3

Thanks :) I already played 1 hour and only got ~200: looks like it will take a bit longer for me xD

I wanted to know the same ; w ;

took me a little less then 2 hours to get all the achievements incl pantsu

2.7 hours I am finaly done C:

Ehi! Some of you want to trade montaro cards with me? I need to complete the badge! ;w;

3 Hours

Around 2 hours totally.

3 hours of only going for panties still dont have it :/

Less than 2 hours to get all achievements, it took a couple extra minutes to get the stickers.

probably took me an hour? maybe a little more than that. it took me 2 hours to get all the achievements.

I have a few more than 802 pantsu

in my case it took me 30 mins, pretty lame game, nothing much to do

2.5 hours so far for me and still havent got the pantsu achievement. got the rest in about half hour-hour though