Goyukkuri nasatte kudasai.= Yukkuri shite kudasai.
"Please relax and feel free to spend as much as time you want."
This expression is typically used when a guest visits someone's home. I don't know if there is an English expression exactly equivalent to this phrase. "Please make yourself at home" is similar but not the same.
It can be also used in the literal meaning, "Please take your time (to do something)."