You're supposed to wait exactly 6 hours in and out game time. Say it's 6 PM right now. So wait until it's 12 in the morning and you'll have either a high tide or low tide. It depends on when you get inside Shoal cave. If it's still a high tide, wait another 6 hours then it should be a low tide.
*EXTENSION*
alternatively (and i'm not sure if this will work) you can try to set your DS time ahead six hours...
You have to go to the Shoal Cave and get four Shoal salt, and four Shoal Shells. To get Shoal Shells go when there is high tide from 9am-3pm, and 3am-9am. To get shoal salt go when there is low tide from 3pm-9pm, and 9pm-3am.
You can find a Snorunt in the Low Tide B1 of Shoal Cave. You can commonly encounter it in Low Tide B3, though, with a 40% chance of appearing.
Go inside Shoal Cave when your in there you should notice the cave is either full of water or it's really dry. When it's dry it's low tide season, when it's full of water it's high tide seaon.
Shoal cave is above Mossdeep city.. It can be dry or flooded depending on the time and tides... there is an old man inside the cave who will ask you to get 4 shoal salts and 4 shoal shells.. during high tide(when cave is flooded) you can get the shells. during low tide (when cave is dry) you can get the salt.. bring these to the old man to get your shoal bell
You will have to evolve it from a snorunt. You can find one of those in the shoal cave just north of Mosdeep city. But you must enter the cave during LOW TIDE. To enter the cave during low tide, you must talk to a fisherman guy on one of the mini islands surrounding the shoal cave. He will tell you that it will be six hours till low tide. Play for six hours or just switch the power of and wait till after six hours then enter the shoal cave. keep going lower and lower in the cave until you enter an icy place. Then, run around and hope a snorunt appears. They are fairly uncommon.
On B3F of Shoal Cave(Low Tide)
The Tide is low in the afternoon i dont now if it is real time or game time
The tide shifts at 9:00 in-game every day. Source: Prima's official guide
Every 3 days the water flow changes in shoal cave check the cave each day to see.
in the shoal cave during low tide tides change every 6 hours
According to my findings shoal cave changes either every 3 hours or 3 days keep going into shoal cave until the low tide is there. According to the Bulbapedia, it is every 6 hours that it is either hi tide or low tide.
You have to wait for high tide.
depending on the time the tide will be higher meaning the cave is flooded during that time you can get shoal shells
In the Shoal Cave, you may come across two exclusive items - the Shoal Salt and the Shoal Shell. There are about four of each at any given time in the cave and together can be traded for a Shoal Bell. The problem is: how do we get the other when we already have one? The is simple: we must visit the cave at the right time. Shoal Cave operates on a timetable. At a certain time each day, the tide in the cave changes from high to low and back again. What this means is that when there is a tide in the cave, a certain section of it is cut of and cannot be accessed until the other tide is in. If it is high tide, then you will find that the cave is filled with water and places high up in the cave are assessible. However, it blocks off the lower entry points to the other parts of the cave. It is only when low tide has come that you can access these areas - but then you can't get high up anymore. Between 9am and 3pm (according to the in-game clock), the cave is in high tide. This is when, if memory serves me correctly, we can gather Shoal Shells. It also reaches high tide between 9pm and 3am. From 3am to 9am, the cave is in low tide. This is when the other 'Shoal' can be found - the Shoal Salt. Note that low tide is also between 3pm and 9pm. This tide timetable' applies to both Ruby and Sapphire (and possibly Emerald).
I'm not really sure when it's low tide, but when you start the game if you set your clock as, '6:00pm', then the whole entire time you play, the tide is low.
You cant get snorunt in leaf green,you must get it in Ruby/Sapphire/Emerald and trade it,snorunt is found inside the shoal cave when its in low tide
You can find it in shoal cave during low tide.