is there a best time of day to sell bitcoin during the day in the uk? I imagine the trading hours of the us and china push the price up at certain points in the day.
Analyzed the situation and make your own trading analysis with the help of other factors such as, other's trading analysis, speculation, expected news, volume established on the day etc. No need to pinpoint the specific time of the day to sold bitcoin since it's not part of the factor. If you noticed that trading hours in China and US push the price up it doesn't mean it's a big factor.
If you still not satisfy then make a monitoring at your time during US and China trading hours and see if your assumption is true.