Grandpa Walton is celebrating his 73rd birthday, and the year is 1935, which means he would have been born in 1862. However, after he dies his grave marker shows he was born in 1865.
The sound of Grandpa/Zeb hitting the floor is heard twice, once a couple of seconds before he falls and once when he actually hits.
The calendar on the kitchen wall seen at 11:00 places this episode in January, 1935. Since the average low temperature in January in that part of Virginia is 26 degrees, the family would definitely not be planning on moving critically ill Grandpa outside to a tent.
It's quite hazardous to have candles in a tent, especially if there is someone bed-ridden in the tent.