Absolutely. As scompa said, the System menu will contain Preferences, and in there you will find Sessions. That window will allow you to set up programs to run every time you start a session.
As for running programs at a specific time, there is an excellent utility called "cron" that is always included by default that lets you make things as intricate as you'd like (you can, for example, make it run every 10 minutes except on the hour every second day of the third week of every fourth month, if you'd like).
Setting up cron is done by running "crontab -e" (this will edit your personal crontab file). What to put in that file is up to you, and the syntax to use is very well documented on the web. As an example, if you want to run "custom.sh" every hour, on the hour, without producing any output, you'd enter this:
0 * * * * custom.sh > /dev/null