So it seems that the maintenance will turn of HTTPS, not that it's unavailable during the maintenance.
> Immediately after the maintenance, users will only be able to access Public PAIR through URLs beginning with HTTP, such as http://portal.uspto.gov/pair/PublicPair. Past URLs using HTTPS to access Public Pair, such as https://portal.uspto.gov/pair/PublicPair, will no longer work.
Immediately after the maintenance, users will only be able to access Public PAIR through URLs beginning with HTTP, such as http://portal.uspto.gov/pair/PublicPair. Past URLs using HTTPS to access Public Pair, such as https://portal.uspto.gov/pair/PublicPair, will no longer work.
> Immediately after the maintenance, users will only be able to access Public PAIR through URLs beginning with HTTP,
So it seems that the maintenance will turn of HTTPS, not that it's unavailable during the maintenance.