Block a steam game from myself for a period of time
As you will have access to the account you will pretty much always have easy access to the game, The easiest ways to do it on your own without any third party scripts etc are to:
Delete the game; without local content you won't be able to play it. You can always download it again at your leisure. You can then selected Installed from drop down menu under Games to only show your installed games, I actually forget about a lot of games I have because of this (although not on purpose).
Ask Steam Support to permanently delete the game from your library, however this will mean you will lose it forever unless you repurchase it (or add it again if it's F2P). Not an ideal choice for a temporary measure.
When there is a game update allow it to download a small %, then pause the download. Change your settings to stop automatic updates for that game; the option should be in that game's Properties on Steam. You can also set all other games (which is the case to Default) to not allow background downloads, so that it won't update that way when you're playing something else. The benefit here is that you can't play the game until the update is complete, the downside is you need to wait for an update. If it's Payday 2 then you'll have DLC released every 2 days, so that won't be long (joke! ;) ).
Use Steam Family View - With Family View you can restrict content, pretty much like a parental lock (which is kind of what it is). The only drawback here is that you know the PIN code so could easily bypass it, and if you forgot the PIN code you'll need to contact Steam Support to access restricted material! For details on Family View see here: https://support.steampowered.com/kb_article.php?ref=5149-EOPC-9918
Forget, or deliberately don't use, your login details for Steam. If you can't access the client then you won't have access to the game. The downside here is that means you don't have the client for any games.
You can right click on a game in your library and select "Set Categories". When you do this, there is a "Hide this game in my library" check box.
If you then want to see the hidden games (to unhide them), click on the filter next to the search box in your library screen (the one where you can choose "Games"/"Installed"/"Recent" etc)
It's silly but you could encrypt the file system of that game, give the encryption key to a friend/your mum and tell them to not give it back to you until 'x'; be that you've done your homework or whatever you're trying to get yourself to do.
A better idea would be to look into how to increase yourself control.
You could always give your login details to somebody you trust such as a family member, who can then change them and agree a time when you can have them back.
I know somebody who did this and it worked for them, it is the best way to avoid temptation.