You want to know when to go clamming?
Go here: http://co-ops.nos.noaa.gov/gmap3/ Scroll the map up to Alaska. Zoom in on the Kenai Peninsula.
Or here: http://alaskatides.com/
Either way, check the tide for Nikiski and Seldovia. Split the difference, as Tuxedni Bay, and Polly Creek that runs into it, is roughly halfway between them on the Alaska Peninsula.
Or take the shortcut and look up the tides for clam gulch, because it's roughly across the inlet.
Like here: http://alaskaoutdoorjournal.com/References/Tides/clamtides10.html