How long should it take to create quality SEO content for a product?

I am pretty new to SEO (like 4 months with no previous experience new) and prior to this job, I worked in a very different industry for a long time. I'm aware that my first 3 hurdles will be learning SEO, learning about the product itself and being able to write at a decent pace.

However, I work for a small (very small) company so along with SEO, I'm also responsible for customer service through email, phone and walk-ins as we do have a tiny store front. I'm also responsible for logistics, shipping and any issue with deliveries like looking into lost packages.

While mostly understanding, I sometimes feel like my boss expects too much from me on the SEO front. It's hard to get into a proper 'writing zone' let alone concentrate long enough to learn something when I've got email or phone going off or a customer is coming in.

It seriously can take me up to 5 days to create a solid 600-800 word product page.

Is there anyone out there that does all this? How do you find the right balance? Is my boss expecting too much of me or am I just being a baby?