Measure the transaction latency or waiting time for transactions via private channels

Dear All,

One question bothers me. The transaction latency or waiting time has been an important factor of consideration for submitting bids for transactions via the public mem-pool: https://ethgasstation.info/. But how about the private channels? Can we measure or draw any conclusion about the transaction latency or waiting time via the private channel? For example, is the median transaction delay lower or higher than transactions via the public mempool? Is there an upper or lower bound on the transaction delay that actually recorded on the blockchain via the private channel?

Thank you so much!

Sincerely. ,
Sunshine