What beliefs would we consider reasonable for a self proclaimed Christian to hold?

[He lives]

This was done over a very long period of time.

Oh?  How many days are we talking, here?  

Adam and Eve had a lot of children over their long lifetime on the earth. After the flood the lifespan of man was still much greater than today and families were large. The Bible does not have a timetable.

There was no adam, and no eve, and no flood.  Much of magic book may be without a timeline, but..."creation" doesn't appear to be one of the parts that this applies to.  

Suffice it to say that it took the necessary time needed for the creation to take place.

Suffice to say, indeed, lol.  That's why I asked how many days would be necessary to accomplish 20, 21, and 21..according to magic book?

The Bible is not a magic book. You should be aware that the days you are referring to in the book of Genesis were not earth days and were mentioned before the sun and moon were put in place on the fourth period of time called a day:

(Old Testament | Genesis 1:14 - 19)

14 ¶ And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:
15 And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.
16 And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also.
17 And God set them in the firmament of the heaven to give light upon the earth,
18 And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good.
19 And the evening and the morning were the fourth day.

The days of creation were not earth days.