Reddit reviews A Practice Grammar of German, New Edition

Lehr- Und Ubungsbuch Der Deutschen Grammatik by Dreyer Schmitt English Version

The following book is from B1 to somewhat beyond B2, so this is probably the right one for you. It explains things very clearly and has a large number of exercises.

Dreyer and Schmitt (2010): A Practice Grammar of German. Hueber Publisher.

See here, for example:
https://www.amazon.com/Practice-Grammar-German-New/dp/3193272558

If you can get only 1 grammar? "Lehr- und Übungsbuch der deutschen Grammatik" (this is the same as this one - with the explanations in German for the first one and in English for the second; Some pages are visible here; the answer key is the same and separate from the books). It is tagged as A2-C1 although there is very little for A2 and it is not deep enough for complete C1 :) That's the grammar I used when I studied German back in the stone age (a much earlier edition of it); that's the one that is the most helpful now that I am in recovery mode. Its natural successor down the road is this one which is tagged as B2-C2 but is indeed a C grammar :)

I would still recommend a textbook series if you can afford one - I had been using Begegnungen and Erkundugen to restore my German and they are pretty useful - look at the content of Begegnungen B1 and see if you need it; or just start with Erkundugen B2. They have their audio and answers included so you just buy 1 thing per level. They also will structure your studies a bit.

Also - there are a LOT of online exercises to give you some more practice. I posted this a few days ago so take a look - ignore the A1/A2 material of course. None of those require codes from textbooks or anything :) At this level, you won't find many courses online but there are exercises and guides.

1. Grammar. Get a book which explains the grammar with exercises. I used this book. With your time frame, I think you should try to invest 2 hours each day.
   
   
2. Practice. Spend at least half an hour every day listening to German TV/news/radio/whatever. When you hear a word you don't know, pause the TV and look it up. Read a German newspaper or magazine every day.
   
   
3. Vocabulary. Install Anki on your phone. Use it whenever you have a couple of minutes to spare during the day. At any point when you're doing your exercises or practicing and you find a word you don't know, add it to your Anki deck so you are continuously practicing it.