I shall leave mine in until the 20th November, six weeks from insertion.
Taking out to the nearest DAY is simply not necessary - one or two, or a few, days either way is not going to risk the end of the world. That is why they quote the time in weeks. If OK to the nearest month, that is what they would quote; if to the nearest day, they would have quoted 42 days.
Think about it. An analogy might be food ‘use by dates’. Perishables are quoted to the nearest day, as the nearest week (end date) might mean spoilage (or eating before bought!) while ‘non-perishables’ have a use-by date (or often ‘best by’) to the nearest end of month.
That is why the average of one and two is two - not 1.5.
1.5 is the average of 1.0 and 2.0, for those that might not grasp this simple rounding system.