Designing difficulty is pretty challenging. You have to know who you want to play your games, and how to make levels they wouldn't find too easy, but also wouldn't get too frustrated on. Personally, I tend to make games that are way too hard, which as I understand it is a lot more common. But a game that's too easy is better than a game that's too hard, so you're on the right track I suppose. Just take this from someone who doesn't play very many puzzle games: These levels are stupid simple.
some players struggled with the time limit
Time limits are kind of artificial difficulty imo. It's like putting an invisible spike at the end of the level. Does it make the level harder? Sure. Does it make the level better? No. Time limits aren't all bad, I just don't think you should rely on them as the only challenge.