Over the weekend, many investors will have time to spend in front of their computers. If the price of BTC goes up, they will have time to buy encryption, so this is also a good time to invest.
Actually most of the people who are related with bitcoin have their day job or business, therefore they find it difficult to give good time to trading on other day, they have enough time on weekend to study the market and do some investment. That is why for most of the time we can see a good increasing in bitcoin price on weekend.