I'd suggest to stick with 365 days in a year and 52 weeks in a year. If they want you to use 365.25 or 52.14 or 52.18 they'll say so.
The only thing to remember is that if you need to convert months to weeks, DON'T multiply by 4 or 4.5 or anything like that. It's too rough. To convert months to weeks, divide by 12 to change months to years and then multiply by 52 to change years to weeks. Much more accurate.