Check the official website:
https://www.canada.ca/en/immigration-refugees-citizenship/corporate/publications-manuals/operational-bulletins-manuals/permanent-residence/express-entry/invitation-apply.html
It states clearly-
“Examples of change in circumstance that would impact a candidate’s CRS score
Changes that could increase a candidate's CRS score:
Graduation from a higher level of schooling;
Reaching an additional year of Canadian work experience;
Obtaining a certificate of qualification
Improved language test scores.”
CRS is always re-calculated on the basis of the documentation you submit. Nobody will judge you on the basis of ITA, unless your CRS drops or you are found ineligible after your documents have been reviewed.
Regarding work hours,
Again follow the official website:
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/express-entry/eligibility/canadian-experience-class.html
Take into consideration that it states-
“We don’t count any hours you work above 30 hours/week.”
Which means- if you have worked 50 hrs/week for 8 months (total of 1600 hrs), they’ll calculate it as 30 hrs/week for 8 months (total of 960 hrs).
Eventually, it ends up being exactly 1 year of continuous work experience.
If you can achieve that by the date your ITA expires, you can easily submit. And based on the first half of this post, you are supposed to be safe.
If you can’t achieve the work experience by the date of expiry of the ITA, I would still suggest not to decline the ITA. You can just let it expire and your profile goes back into the pool and is eligible for the next relevant draw.