I don't have an answer to your question, but I happened to come across this discussion on the vegetable forum, which has photos that look like your eggplant. Since it seems no one reading the Texas Forum right now has grown Ichiban eggplant or they would have replied, maybe the vegetable forum would be a place to ask.

If you find out let us know. Wishing you the best.

Yes that beautiful eggplant is ready to pick. When you cut it you can
see the seeds, and if tender the seeds will be small and white in
color. As it matures the seeds will harden and change the color to
brown. I usually pick them when they are tender than this and it will be
tastier.

By experimenting you can find out when to pick them so that they are the tastiest. Enjoy,Chitra

That does not look like an Ichiban to me, more like a Ping Tung. But yes it is ready to pick.