It could be either, Ms. Jandi. There is no indication of how much overtime (notice that 'overtime' is uncountable) or when it was worked. All we know is that an unspecified number of extra hours were put in during the week.
If this is within the U.S., where a 40-hour week is standard, it means: Our company had us work more than 40 hours last week.
There is no way to know from this if the extra hours were worked only on one day, on two days, on three days, ..., on all the days of last week - nor is there any way to know how many extra hours were worked.