How can i be sure that after successful payment ebay will let me use the one second prior to bid expiration option. Because now when i want to use it, i see it is in an experimental mode.

Hello Nickolay,
Thank you for your question about the 1-second option. That text was not supposed to be there as the feature is no longer experimental.
Thank you for taking the time to write in. Please let us know if you need any other assistance.