i am planning to apply for a double entry visa, can i request for a 60 or 90 day validity?

A double-entry visa is generally valid for 6 months. The validity is the period from Issue Date to Enter Before Date. I guess you want to ask for the stay duration per entry, 60 days or 90 days. You can request for a double entry with 90 days stay duration per entry. The final decision is up to the visa officer.