It's largely up to you when you create an ORCID identifier or even if you you do. Basically, it's a way to trace all of your future publications back to a unique identifier which is arguably very useful considering the massive number of articles available online and the likelihood of authors with similar names.
You can even register and ORCID ID after publishing and retroactively add your existing publications. However, it will be easier to keep track of them as you publish them. I created an ORCID ID after attending a library seminar recommending them at the beginning of my postgraduate studies, it didn't take very long to set up, and wasn't an issue sitting idle before I before submitted publications.
Another consideration is that some journals (e.g., BioMed Central journals) integrate with an ORCID ID in their submission portals. I'm not sure if they require them but it will at least save you considerable time entering contact information with each submission. So it will save you time when it comes to submitting publications or tracking them later but there's no harm doing in advance or leaving until you submit an manuscript (to a journal that recommends them).