How is the LTP of stocks on the changing over the weekend when the market isnt opened?

for example all stocks within the NEST terminal have changed since market closed.

The LTP and the closing price is usually different, check this question

If you have seen some changes in prices on the trading terminal over the weekend it could also be because of some mock trading that would have been conducted. Mock trading to test the systems and those are not real prices. 

Thanks Nithin! MOCK trading is done by Exchange or Broker?

exchange conducts it and brokers participate testing any new products that they might have.