Some chairs or sitting positions will cause a sciatica flare up either instantly or within a few minutes. The skill is in noticing which. That said, it took some time and effort for me to be able to sit at a desk for any length of time. I used standing desks exclusively for years.
For me, stretching and movement is what helped mitigate my issues as well as weight loss. It can't hurt, but I can't say it's a panacea for everyone. All of the cases of sciatica that I'm aware of are fairly unique in terms of how people find relief.