The National park Bohemian Switzerland in Czechia is situated only 1 hour by direct train from Dresden. You can look at Deutsche Bahn https://www.bahn.de/ and find right time.
Number of direct train S1 and going generally every hour. You will get off last Schöna. Schöna is only train station and ferry port (not village). You will get on ferry (going every 10 min) to Hřensko.
Village Hřensko is starting point to Pravcicka Gate or Edmunds Gorges. There are many restaurats, hotels and also vietnamies market (generally for German tourists). You need to walk throught village Hřensko along river Kamenice. For better orientation look map down.
I can also watting in ferry port Hřensko and manage tour with you like guide.
You can arrive any dates of year. The Nationa park is open whole year for hiking. Only boat atraction in Edmund Gorges is open generally from The Easter to Halloween.