What am I doing wrong when I reply to viewing requests?

[Josh L.]

I started seriously posting to zillow and trulia and I keep getting the same message which I'm assuming is a automated request by people interested in the rental:

"I am interested in this rental and would like to schedule a viewing. Please let me know when this would be possible."

So I reply to this request with something along the lines like:

"Hi (their name),

I can schedule a viewing tomorrow. Will 6PM on Thursday work for you?"

Am I doing something wrong?

I throw out this time because I'm trying to set up a time so that I can bunch up all the viewings around the same time so I don't have to drive back and forth and to let the applicants see that there are other applicants interested too. 

And, I'm responding to the email within a few hours after the request and try to set a viewing for either tomorrow or that day if I have already have set up a viewing for that day. 

But, after I respond, most of the time I don't get a response back. Maybe, 1 in 4 will confirm that they would still like to schedule a viewing. 

Should I be responding in a different manner or something to get more people to follow through after their initial request? When they respond, their telephone is also given. Would calling them to schedule an appointment rather than replying via email make a difference?