I would ask your agent to ask for seller to respond within 24 or 36 hours after receiving. It's normal but nothing unethical about your situation But the pressure is on the seller with placing a time frame and also sends is a message that your a serious buyer. Of course alot depends on seller agent and how he presents the offer. The seller will pick up any and all attitudes an agent carries to the table for consideration. HOpe this helps. As I have always told my clients if this doesnt work out then we keep searching for another property.