ACS validity - 24 months
ACS validity is 24 months from the date of issue. The validity is mentioned on the ACS letter too.
Submit EOI now and Keep Current Employment END date blank
My suggestion is to submit the EOI now and keep your current employment’s END date BLANK in EOI.
This way, EOI will automatically keep adding your work experience and will give you extra 5 points as soon as you reach 8 years experience.
Just make sure that you do not change employer during this time. If you change employer, you will need a new ACS assessment.