what showes time lapse?

I'm not sure what you mean by "time lapse". Can you explain?

There are several passages which indicate that time has passed.To quote directly from the book, the following phrases all appear in a description of Jack... "His sandy hair, considerably longer than it had been when they dropped in, was lighter now... Except for a pair of tattered shorts..." Ralph and Simon are attempting to build a third shelter, none of these were mentioned in the earlier chapters so time has obvious passed if three have been built. Ralph says, when talking about building shelters to Jack, "Been working for days now. And look!" Ralph also talks about meetings and says, "Meetings. Don't we love meetings? Every day. Twice a day. We talk." Ralph is also described as having a "Tangle of fair hair," an obvious reference to its growth. Simon is described, in further indications of the passing of time..."The coarse mop of black hair was long and swung down... He wore the remains of shorts....and, Always darkish in colour, Simon was burned by the sun to a deep tan."