If you look at the bottom right part of the image, you will see that time difference cannot be uniquely determined from declination. Declination will narrow down the time difference to two times of year, which have very different time differences, but you will need some other information to determine which of the two times of year it actually is.
For example, when the declination is neutral, at the equinox, it may be the spring or autumn equinox. Those two times of the year have different time differences - one is plus seven minutes while the other is minus seven minutes.
http://upload.wikimedia.org/wikipedia/commons/1/12/Equationo...
If you look at the bottom right part of the image, you will see that time difference cannot be uniquely determined from declination. Declination will narrow down the time difference to two times of year, which have very different time differences, but you will need some other information to determine which of the two times of year it actually is.
For example, when the declination is neutral, at the equinox, it may be the spring or autumn equinox. Those two times of the year have different time differences - one is plus seven minutes while the other is minus seven minutes.