Most words that I have trouble with I can eventually get if I rack my brains for my mnemonic for 30 or 45 seconds but I am not sure if this is the correct method of learning or whether I should be marking a question as “missed” if I can’t get it in 5 seconds. As I progress through HSK4 I find these situations arise more frequently and would like to avoid adopting bad study habits if there is a best practice in this regard.
If you aren’t bogged down with lots of reviews, and don’t mind extra reviews, the stricter you grade yourself the better. If you feel you’re “failing” because you don’t remember it within a certain time frame, I would personally mark it wrong. I’ve been in the boat of no such thing as “so-so”. It’s either wrong, or it’s correct. With that said though, if you’re finding that there are a lot of reviews to keep up with, you might want to mark it correct since you did remember it (unless you think you’ll forget your mnemonic by the next time the review would happen).
Let the tool do the work. If you don’t know it, just fail it and let it repeat. If you’re taking 60 seconds you could be hitting the eyeball, practicing drawing it, reviewing 4 other words, and then reviewing the trouble word again in the same time.