To dwell in the here and now does not mean you never think about the past or plan responsibly for the future. The idea is simply not to allow yourself to get lost in regrets about the past or worries about the future. If you are firmly grounded in the present moment, the past can be an object of inquiry, the object of your mindfulness and concentration. You can attain many insights by looking into the past. But you are grounded in the present moment.
Mindfulness is simply being aware of what’s happening right now without wishing it were different; enjoying the pleasant without holding on when it changes (which it will); being with the unpleasant without fearing it will always be this way (which it won’t)