Depending on the length of contract until settlement, we recommend you leave a minimum of 14 days to have an answer - not because it takes this long to book an inspection, but you still need to consider the outcome of the inspection. If you find there are queries that you want answers to, or negotiations you need to have after you've seen the report, you still have to meet the timeframe you've nominated in the contract before your sale is unconditional.
Solicitor, Tim O'Dwyer says "The Real Estate Institute’s and Law Society’s joint standard residential contract used by most estate agents makes provision for a “building inspection date” and the name of the “inspector”. (If no date is inserted, the contract is not subject to a building inspection report and the inspection clause does not apply.)".
We recommend you ask your estate agent to take Mr O'Dwyer's comments into consideration when drawing up your contract for purchase and be realistic with building inspection timeframes.