Once you have the map from the seal island, and the peanut butter crackers from playing Hangman (Go To Jail) against Nate, you can use Spitsy the dog to dig up the Time capsule, which is right where the girls were standing, in the open section of the playground.
Place the crackers on the ground, then click on the box when it comes into view. You can't take it all the way out : just click on the shiny clasp to open it.
On Big Nate island the three girls stand on the playground to the right of the school .
Fixing and ringing the bell is the second-to-last stage of the island. Once you have the map to the location of the buried Time Capsule, you can use the peanut butter crackers to get Spitsy the dog to dig it up. (Note : it will not come out of the hole - push the clasp.) (see related questions)
The treasure on Big Nate Island is in the long-lost Time Capsule. (It is actually in the playground, where some girls are at recess. To get it, fix the school bell and ring it. The girls will leave, and you can use Spitsy the dog to dig up the Time Capsule. (Give him a peanut butter treat and he buries it.)
to get the girls away you ring the bell
Recovering the Time Capsule is the object of Big Nate Island. It is actually buried under the Playground...there are some girls at recess standing right on top of it. But it is not easily uncovered. Knowing where it is (under the talking girls at the playground) does not allow you to dig it up. You still have to find the clapper, fix the bell, and locate the map to the capsule. (see the related question)
You put the peanut butter crackers on the floor where the girls were and you have the dog come and dig it out.
pop
its where the talking girls are standing
near the playground
Under the playground
where the chatty girls are.
You will first have to have these things: a stink bomb, bubble gum, a bell clanger, and a lobster. You use the lobster as a wrench to unscrew the light in the lighthouse which will scare away the bird the you go up onto the top of the school and put the bell clanger on the bell and it will ring.