Yup - it takes time, resources and men to achieve it fully.The massive danger for Ukraine...and it's why they won't go too far too soon...is that they risk being encircled in a Russian counter attack. They have to broaden the breach and get a lot of men and heavy equipment through to make that sort of big land advance stick. That's why any gains will be painfully slow and why Tokmak 20km to the south isn't going to be within reach in the late autumn and winter.
However what is the other option? Freeze the battle lines and enter into an uneasy truce with Russia?
Russia will simply rebuild its armed forces and go again at Ukraine in a couple of years. Ukraine has to fight on, it has to achieve a breakthrough and then broker a peace.
What comes after that is another story (NATO membership or NATO protection force)?