Does UC claim date start when I start filling out the claim or at the end?

Hi, I'm migrating from ESA (support group) to UC. Reading though the comprehensive B&W guides it's not made clear when the date of my claim actually starts. Does it start when I start filling out the claim form or is there a 'submit'; button at the end of the form and the date of the claim starts only when I press the final submit button at the end? Also, Can I take my time filling out the online claim form (over the course of a week or two, but obviously before the deadline date) or do I have to complete the online claim form in a very short timespan? For health reasons I can't rush anything.

Also, before I press any such 'submit' button, can I go back though my claim and reread what I've written and revise things if necessary, or as each page is completed is it cast in stone?

Thanks in advance for any advice.

Ali.