I would recommend the book: Edwin R. Taylor and John Archibald Wheeler, Exploring Black Holes: Introduction to General Relativity, 2000, Addison Weslay Longman. Specifically, pages 2-28 to 2-31 discuss gravitational effects on time.

In the following dt[Infinity] is a time interval measured by a stationary clock at infinity. dt[r,M] is the corresponding time interval measured by a clock at a relative radius r to the radius of the black hole horizon. So putting r==2M would correspond to being at the black hole horizon.

dt[r_, M_] := dt[Infinity] Sqrt[1 - 2 M/r]

The following plots the time interval of a clock at radius r relative to the interval measured by a clock at infinity.

The time interval goes to zero at the black hole horizon (r = 2) so you can get values as small as you want. For example, at r = 2.0001 we obtain:

dt[2.0001, 1]
0.00707089 dt[\[Infinity]]

As the clock is moved further and further out its time intervals get closer and closer to the clock at infinity.

Yes, that's how many seconds would pass on the clock that near the event horizon compared to 1 second passing on the far clock. And even less time would pass as you got closer. At r = 2 no time would pass. But to make a good book you should get the help of an interested physicist. Maybe like Lawrence Krauss at Arizona University.

And I bought that book for $37.50 at Border's Book Store sometime after 2000.

Dear Jofre,

Thank you for your reply. I don't see your response on the website but I did get an email. Unfortunately, I must be doing something wrong. My input is this:

1. time in rest frame (what or where is the rest frame?): 90 years
2. gravitational acceleration: 1.52 x 10^12g
3. radius: 30km

My answer is -1.423 x 10^9 i seconds. I don't know what i means, and I'm not seeing where I wait 63 years to watch my friend age 90 years. It also contradicts an astronomer who only would say I'd wait "less than a blink of an eye." I apologize for the confusion. This subject is a bit thicker than I'm used to :-)