There's no 100% reliable way to filter mainnet and jtoomimnet. The jtoomimnet blocks have different users and different payment addresses (e.g. the 1GuDN address) than mainnet, so you can do it manually if you'd like.
Ohh one other question... The last block was found on the 31st of December... So no blocks both for jtoomimnet and mainnet for the lat 30 days.
Then how does "since the expected time per block is currently around 20 days on jtoomimnet" that apply ?
It's probabilistic. Luck is involved. Sometimes it takes less than the expected value. Sometimes it takes more. It's the same as how Bitcoin has 10 minute blocks on average, but sometimes it takes an hour between blocks, and sometimes it's only 2 minutes.
https://www.khanacademy.org/math/statistics-probability/random-variables-stats-library/poisson-distribution/v/poisson-process-1