It sounds like you’re currently using the Work Time settings for duration which does convert 1 year to 48 weeks. Based on the hours a day, week, and month are set to equal it breaks down like this: 8 hours = 1 day > 40 hours (5 work days) > 1 week > 160 hours (4 weeks) > 1 month. Therefore it sees 1 year as 12 months which equal 4 weeks each.
If you change the duration setting to Calendar Time then it converts 1 year to “52 weeks 1 day”. You can also specify your own custom values as the other poster’s screenshot shows.
As for being able to enter a value and have it display as months, this is not currently an option. If this is something you’d like to see I would recommend emailing us with your thoughts so we can add them to our development database. Hope this helps!