Timer can easily be build around LM555 chip. It is very simple , just a few resistors and capactoors. search the web for the word "lm555 timer circuit" or something.
If you want a charger which automatically goes off when the battery is full then follow this link
http://www.universalhost.de/html_bit/b-charger.htm
It is not very difficult to build, just follow the schematic.
If you use 12v input then value of R!1 should be 800 ohm
and R4 should be 22k not 33k (error)
Value for RSense is 1 Ohm if you want 250 mA charge current, or 0.5 Ohm for 500mA current (or anything inbeetween ). I don`t recommend using greater charge current than 500mA
You can get free saples of MAX 713 and MAX 712 chips at
http://www.maxim-ic.com/