Can you call him now or should you wait was the question right?
So many investors forget that they are actually selling too when acquiring. You are pitching to the seller that he should part with his house for your money. You are selling them on why they should give it to you at a less than market rate. If investors were just buying, they would be paying what the sellers are asking without any negotiating.
Given that, you just learned your first sales 101 lesson. Never leave the current appointment without setting the next one. In some cases you should set it for them and instead of asking what time, suggest two times and let them pick.
Given the information that you have provided regarding his attachment, I would have handled it by saying something like this: ”Mr. Seller, I know this house is important to you and I want you to make sure you are ready to sell it. I do have other properties that I am considering in addition to this one. I don't want to give your money to someone else without giving you a little bit of time to consider it. My final offer will stand for 24 hours and I'll call you at this time tomorrow for your answer."
First you would have established better rapport and more credibility by sympathising with his attachment to the house. It also would have put him temporarily at ease assuring him that you want to make sure he's ready to sell. It helps take the pressure off. Second, you're letting him know that the money is his, but that you could take it away if he doesn't accept your offer. It's just a gentle reminder of the potential negative consequences. Last you are effectively setting the next appointment. By setting the time of the call you've given him a deadline about when the decision needs to be made, and you've given yourself the time that you will have your answer.