If the property is empty and the buyer does not require a mortgage, a sale or purchase can all be completed in a few days but this is very unusual.
However it is more likely that a mortgage will be required and there will be a chain of transactions. If that is the case it usually takes 4-6 weeks to exchange contracts and then another 6-10 weeks from start to finish.
We do all that we can to progress your transaction as quickly as possible but cannot offer any guarantee about timescales!