Inspections are very important upon purchasing a property and I highly recommend that every prospective buyer has an inspection done on their selective property. Although many properties are sold "AS-IS" With A Right To Inspect, meaning that a seller is selling his/her property "AS-IS" in the condition it is in and declares that he/she has priced the property accordingly and will not make any repairs to satisfy a buyer's purchase. However, at least, in the State of Florida (check with your state laws), buyers have a right to inspect any properties whether a property is sold "AS-IS", or not, and buyers may walk away from of a contract if they do not like the results or their inspections (extensive work needed and cost for repairs). .
The time limit for inspections vary from contract to contract. Most contracts have a standard general provision (clause) addressing inspections plus they have addendum and riders for specific inspections (Lead Based Paint, Mold, Chinese Dry-Wall, etc.). Standard contract clauses for general inspections usually have 10 or 15 days default periods for inspections but they also have a blank line to manually add another time period if needed (shorter or longer). Make sure that your inspection periods are consistent with each other: i.e. In addition to the general inspection, if a buyer decides to have a mold inspection, mold inspections are timely because they need to be sent out to labs and after results, it could be necessary to conduct more tests and what not. So, you may want to allow more time for this inspection. Otherwise, If buyers let it be within the same time-frame as the general inspection, they may lose their edge to walk away from their contract on technicality of time and be forced to go through with the sale.
I highly recommend to any buyers to do their homework before they are ready to purchase properties. Call professional inspectors, ask questions about what is involved with specific inspections along with potential costs and time involved. This way buyers will have a better idea of time; then, when ready to write a contract, discuss proper time-frame with your Realtor-Agent.
Even if buyers are looking for fixer-uppers and think "What's the use of an inspection. I'm gonna renovate the house entirely." Inspections are money well spent -- especially on a house -- to make sure the house has good bones, good foundation, condition of plumbing and electrical wiring, a solid roof and that its wood is not decayed by dry-rot or other wood damage (termites, for instance). This way buyers know the whole condition of the property. Sometimes, fixer-uppers can be a money-pit.
DISCLOSURE: I AM NOT AN ATTORNEY NOR A PROFESSIONAL INSPECTOR -- DO NOT TAKE MY STATEMENT FOR GRANTED -- ALWAYS CHECK WITH YOUR REALTOR-AGENT, OR A LICENSED PROFESSIONAL PROPERTY INSPECTOR, OR WITH AN ATTORNEY OR WITH ANY OTHER RELATED PROFESSIONALS CONCERNING ANY INSPECTION CLAUSES OR RIDERS TO UNDERSTAND CLEARLY WHAT IS INVOLVED AND TO ENSURE THAT YOU CAN AND WILL GET YOUR MONEY BACK IF YOU WANT OUT OF A CONTRACT AS RESULT OF NEGATIVE INSPECTIONS.