I'll stay here no less than three days.

no less than不亚于,竟达……之多
not less than不比……差,至少
I'll stay here no less than three days.我呆在这里（的时长）不会少于三天.或我呆在这里的时间长达三天.
I'll stay here not less than three days,我呆在这里至少三天.
两句意义差别不大.但是有一定区别的.看语境了~
希望对您有所帮助~