That's the ticket package my wife and I used - we arrived just before midday, and left around 4pm, and had a pleasant stroll around the grounds, a spot of lunch, the house tour and the Egypt exhibition to finish off. No photos allowed in the house by the way.
There a few places to get food which were quite reasonably priced and tasty, but a lot of people there opted for bringing picnics, particularly as our visit two weeks ago coincided with the warmest day of the year so far in the UK.