it takes longer playing all your games at once. Also, more suspicious and Valve might ban your account. Idle a game 1 at a time to get drops

Due to changes in the refund policy, Valve now requires that games have 2 hours of playtime before the normal drop time for trading cards starts. Idle Master prioritizes getting all STC enabled games to that 2 hour mark before it starts idling for cards. From the quick look at your recent games, you have a lot of STC games with less than 2 hours of playtime.

Glimmer is correct and Jonno83900 is uninformed. With 252 games left to idle, Idle Master will attempt to idle each of those games simultaneously up to the 2 hour mark first (so that they're eligible for card drops) before idling games individually in sequence to earn trading cards.

Steam will only count playtime up to 30 games at a time, so this is the number Idle Master idles at once. This means you'll need to idle a total of 9 batches each for 2 hours before cards will start dropping - so you should expect to see your first card drop within 20 hours.

As Glimmer said, this is due to Steam's new refund policy requiring each game to be idled for 2 hours before it becomes eligible. In the Idle Master settings, you could set it to idle games individually - which in your case would initially be faster to start dropping cards but then each game has to be run for two hours before cards drop - meaning the entire process would take 252x2=504 hours + idling time to complete. So even though you have to initially wait 18 hours for all your games to be eligible, this will save you about 21 DAYS of idling time.

Hope this makes sense!

Got it, thanks for the clarification guys. It's just a larger up-front investment in idle time that I hadn't noticed with the policy changes.

You might consider running a batch or two of games in the default "parallel" mode to reach the 2-hour mark for those games, then switch to one-at-a-time "serial" mode in the settings so you get some card drops for those games, then switching back to parallel mode.

In fact, would it be an idea to have an option in IM to use this algorithm (maybe even by default)? That is, to farm all cards for games that have their 2-hour play times before automatically switching to parallel mode until you have more games eligible for drops, etc.