4 weeks ago I wrote about taking on a 15 minute daily cleaning habit together with my wife. It has been tremendously effective and our home looks like we just moved into it: everything is clean and sparkly, and it even smells nice. And all it takes is 15 minutes per day!
Nice! I slowly learned (some) German ~10 years ago but don't live there anymore, so hardly use it. But since I don't want to lose it, I forced myself to use everyday things (phone, laptop, websites, etc) in German as practically as possible, maybe you'll want to give it a try!
I’m about 2 years into a similar journey with Japanese. My wife is Japanese and we are teaching our son the language, so it’s been very valuable for me to know it too, ちょっと (a little bit). At this point, the time I spend on Duolingo each day is quite exhausting. To really absorb the lessons, I have to focus intensely, and it winds up taking away from my productive time rather than replacing down time. It’s been worth it, but it wasn’t something I was expecting when I started.
I've been learning German as an adult for 3 years and my best advice is to get an online tutor. Duolingo and other apps are nice and tempting, but nothing beats having the realtime feedback of a native speaker that you're specifically paying to teach you. I think the paying part is important because teaching someone a language can be a very energy consuming task. Furthermore, trying to learn from a partner can be difficult if you're already entrenched in one language (this was my experience :). I've seen people fall into the false productivity trap of Duolingo — their streak is long, but their real world conversational skill isn't great.
Previously, I learned Mandarin Chinese using a combination of Duolingo, but also more importantly going to weekly language exchange meetups since I was too cheap for a tutor :)