You may want to see if the Smarthome TimerLinc Relay may do what you want.
http://www.smarthome.com/2456S3T/TimerLinc-INSTEON-Plug-In-Timer/p.aspxI added an X10 address to mine and set up an On and Off timer. It did send the X10 On and Off at the correct times.
Can do 14 On times and 14 Off times. You can pick the whole week, weekend only, weekdays only or individual days for each event.
Quick Guide and Users Manuals Links are on the 2456S3Ts web page. If you care to look at them.
A4 is a local chime module. Timer commands monitored with my 1132CU interface.
R: A4 - 6:10:48 PM 2/24/2012
R: AOn - 6:10:48 PM 2/24/2012
R: A4 - 6:13:47 PM 2/24/2012
R: AOff - 6:13:48 PM 2/24/2012