I saw your other posts so I am assuming this is all related to the same property.
There could be various reasons for not having the open house, but based on the listing agents other strategies (aptmnt only and bids on monday) I am pretty certain the "no open house" is also part of the hype-strategy. It gives the property a more untouchable air and builds the momentum of "must have," "must act now."
These strategies are all an effort to get the highest price. They will hopefully bring in multiple bids with limited time to act (forcing higher numbers ... "no time for low balls") and create mystery between all those bidding (again, forcing people to negotiate against themselves or this unknown "higher" number). This is a great strategy for sellers with great houses but unfortunately a bad one for buyers as the emotions of fear of losing to someone else drives offer prices that are perhaps unwarranted.
You just need to be realistic about the property. Make the personal decision ahead of time of what your best price is and stick to it.