Achievement wise what is the most completed 100% games you got in 1 day?

I did 15 on January the 1st. They were very tiny though as 13 of them were 100 hidden games
There have been multiple times of around 10 but they have also been super tiny to. The most I've probably got otherwise is 2/3 if I did a hog that same day

If you want to count achievement spam games, I did 17 "Achievement Hunter" series games in one day once. For actual games with real gameplay, my record is three, on several different occasions.

...Usually when I finish a game I don't immediately start another one... (Starting stuff is really hard. :/ )
And most of the games I play take more than a day to 100%.

So, yeah... 1.

from legit games - Game Dev Tycoon (https://store.steampowered.com/app/239820/Game_Dev_Tycoon/), but that's just because i had played the game before it was released on steam.
from "other" - The Plan (https://store.steampowered.com/app/250600/The_Plan/)

I don't know, i don't care.

It's done when it's done :o)

Looking at achievement tracker, my record was 9 games 100%'ed in a day, 21st April 2018. Mostly from this list of short free-to-play games.

Since then, a year after I joined SG, where I've been constantly informed about ongoing bundles, my game count increased a lot, and so did my backlog, where I am usually at now when gaming.

Two in a day is the most I've ever managed, but I've done it several times (including yesterday).

Usually it's a case of finishing one longer game and then immediately following it up with a short one, like an Artifex Mundi HOG. Otherwise, it's a case where I go finish up the odds-and-ends achievements on two mostly complete games.

What Lokiator said is usually what happens for me as well.

Even for shorter games 3-5 hours long, that means having to game anywhere from 6-10 hours in a single day.
For people who have jobs, that can be quite a feat.

I've finished 2 or 3 games in the same day a few times(although it's usually games that I started earlier and just happened to finish at the same time), but I've never completed more than 1 in a day, at least I don't think so.
Looking at my profile I've only completed 27 games despite having almost 3000 achievements and having 151 titles marked as "finished" in my library, so I guess I don't even go for completion all that often.

VN is the most easily game to farm achievement, there also H puzzle game too
Just press Ctrl to skip and skipped all the story and you should got all the achievements under 5 hours or less