...I was under the belief that there is really no mathematical/theoretical way to calculate the time-value of an option, other than the fact that usually the time-value decreases as you come closer an closer to expiry. In the end the pricing of the time-value part of an option reflects bid/ask - supply/demand.
When I mention time value I am including the implied volatility that is part of it. So are interest rates. The implied volatility can be calculated and is indeed related to the supply and demand for options. It is currently quite high for TSLA options. For the S&P 500 it is called the Volatility Index (VIX) and can be traded. I sold the $165 strike call at $20.35 to someone who expects the share price to be higher than $185.35 at the close on January 18th. If not, then he loses. If it closes at $165 or under, he loses his entire investment in the options. Of course this assumes he holds until expiration.