i want to set time limits for certain users
 

so when they log on to their profile in kde, they have a max of "x" hrs per day, but not necessarily on any set schedule. can it be done?

I found timekpr which looks like it may do the job. One problem you may find is that it says it is heavily dependant on Pam which is not part of standard Slackware - may be worth a look anyway.

according to the website it's no longer maintained

Yes - I saw that but that doesn't mean you can't run the last edition of the code. As I said I think the problems may well be the reliance on Pam which Slackware doesn't run - it would probably mean installing Pam which could be a pain. Instructions are here should you want to try.

i'll try a crontab approach first, but i would have thought slackware would have tools for this.

Some time ago I used KChildlock to do this. Not sure what the current status is.