Can someone tell me when the hash rate chart figures are set each day?
During the day they change constantly & I'm wondering if there is a set time of day the value for that day is set?
Who records it (I assume automatically). Are there different keepers of these statistics (multiple site each recording there own) or one official record?
The hashrate (it's an estimation) can be calculated directly from the blockchain using difficulty and time of blocks (basically it's "work" divided by "time"). Note that the estimation is (by design) highly error-prone. You can't get an exact value for a point in time (not from the blockchain at least), but only an estimation over a period of time.
Look for example at
http://bitcoin.sipa.be where you can see 3 differnt periods being used in each graph.
For example the green line in
this graph from the linked page is average over an 8-hour period. If it was correct data, it would mean the hashrate fluctuates up to 100 TH/s throughout one day. (~30%). That's most likely not the case, it's mainly bad/good luck of the miners (poisson-distribution).
