This app was mentioned in 16 comments, with an average of 5.75 upvotes
There's an unofficial Android GDQ app that I've been using for a year or so - works well, allows you to set reminders for specific runs, shows the schedule, pushes info about the runs going on now/donation total etc. Might want to reach out to that dev and see if you can collaborate?
https://play.google.com/store/apps/details?id=com.shuneault.agdq2016&hl=en
Not a calendar but Sébastien Huneault's awesome Android app, SGDQ 2017 Schedule, for keeping up to date with the schedule, setting/getting reminders of when a run starts, etc.
Don't know if there's an iOS version — I hope there is because it's immensely useful.
There's also the stellar Android app: https://play.google.com/store/apps/details?id=com.shuneault.agdq2016 (don't let the ID confuse you, it's not for 2016) which usually has updated schedules, can alert you of the runs you want to watch, etc. There might exist an iOS version also.
The GDQ Schedule (Android) app seems to be updated for this AGDQ as well. Huge thanks to the dude that makes and maintains it! I've used it every GDQ since he started doing the app.
https://play.google.com/store/apps/details?id=com.shuneault.agdq2016&hl=en
The guy who made this app posted it here on /r/speedrun a year or 2 ago and has updated it for every event. You can also adjust the settings to display current game in notification and even have an alarm for an upcoming game you want to watch. I use it religiously every event (I wish I could remember the /u/ profile for the guy who made it).
I built an Android app just for that: https://play.google.com/store/apps/details?id=com.shuneault.agdq2016
Here you go. Sebastien enabled it again today. GDQ schedule Android app
If you have an Android phone or tablet: https://play.google.com/store/apps/details?id=com.shuneault.agdq2016
Not sure if an iOS app exists, but maybe someone else can chime in about that.
There's a free app some awesome guy put out that shows the schedule, and you can set alarms. https://play.google.com/store/apps/details?id=com.shuneault.agdq2016
https://play.google.com/store/apps/details?id=com.shuneault.agdq2016&hl=en is the app I use, was just updated for AGDQ 2018 today
This app does exactly what you're looking for :) https://play.google.com/store/apps/details?id=com.shuneault.agdq2016
There's an app that's usually updated before each GDQ. It's really slick and nice: https://play.google.com/store/apps/details?id=com.shuneault.agdq2016 (don't know if there's an iOS port).
Friendly reminder this app exists and it's amazing
https://play.google.com/store/apps/details?id=com.shuneault.agdq2016
I disagree. If you have an Android phone https://play.google.com/store/apps/details?id=com.shuneault.agdq2016 is far simpler.
Edit: lol at the single downvote.