Japanese Maple repot to bonsai pot

Hi,
I bough this Japanese Maple last year and winterized it in a unheated garage over the winter. I am in zone 3.
The upper part of it died off so I cut it off. The main stem (Trunk) is just over 1"in diameter and is about a foot tall.
I would like to see if I can turn it into a bonsai.
It is now in a 5 gallon pot. Is it save to trim the roots to fit into a bonsai pot? When is a good time to do it?

Tips and recommendations is highly appreciated

I would grow it in a big pot a few more years. When you decide to put it in a small pot, do so in late winter or early spring.

Tropfrog wrote:

I would grow it in a big pot a few more years. When you decide to put it in a small pot, do so in late winter or early spring.

Thank you!
Late winter/early spring means before budding in the new growing season?

fishlover wrote:

Tropfrog wrote:

I would grow it in a big pot a few more years. When you decide to put it in a small pot, do so in late winter or early spring.

Thank you!
Late winter/early spring means before budding in the new growing season?

Well the optimal time is just before it is budding out. Just hard to tell before it happens. I have done it successfully in februari, here they don't bud out until mid to late may. I guess most of the winter would be ok.

What is the rush? Do you not want to develop the tree more?