I hunted tdal marshes for over 20 years before relocating to E.WA.
Before hunting a tidal area, go out on a low tide to see the lay of the marsh BEFORE the high tide comes in. Tidal ditches and marsh depressions become invisible when under saltwater. I watched many an ignorant rookie go for swim or even momentaily disappear beneath the water because he thought the marsh under the water was as flat as his back lawn. Obviously, you need to wear a good pair of waders; even hip boots just won't cut it.
Once you know the lay of the marsh at low tide, attempt to hunt it on an incoming, preferably mid-morning, high tide. The ducks will generally come in with the water; so you want to hunt the water's edge or the water itself as the high tide comes in. If the high tide isn't too extreme; you can hunt it all the way through slack tide until it starts to pull out. The birds will become nervous with the moving water and fly at this time, as well.
I liked to set my decoys on the dry marsh of low tide and wait for the incoming high tide to float them. As mentioned, on the right high tide I would wait it out; however, if the rivers had been flooding and the tide was really running...I'D GET OUT, ASAP!!!
Thus, NEVER HUNT A TIDAL MARSH W/O KNOWING THAT DAY'S TIDES!!!
Good luck, I learned all of the above on my own. Hopefully, those tips will help you to enjoy yourself.
Tom