Impending Site Merge - Ideal Time Frame

[Shop-Sq]

Hello Moz Community :)**Back Story:**For the past 8 years, we have been running our main e-commerce site on Magento 1For the past year, we have been building out a new far superior version on Magento 2The new Magento 2 site is essentially done we have a couple little last tiny tweaks/improvements to complete. All signs point to it being 100% done by January 31 - 2019. The new site is currently totally functional and fully operational you could complete a checkout no problem. We currently have the site blocked from being crawled. Although we have rewritten all the site content & taken all new photos we've been concerned with duplicate content issues.
I have attached an image that is a very good representation of our average sales pattern in a typical year. We are a seasonal business so there are big highs and lows. **Concerns:**My hopes were to launch the site around March - 1 2019. I have to 301s meticulously prepared in a spreadsheet and ready to go. My concern though is making this change right before busy season is about to hit. On the other hand though there really never is an ideal time to make the change as cash flow is equally important if not more important during the slow season.Ideally, I would allow the site to be crawled and run them both in tandem for a while but I'm concerned about potential duplicate content issues even though the content has been significantly altered.**Main Question:**What's my best bet?1) Do the 301 in March and hope for the best2) Allow the site to be indexed - risk duplicate content problems and run them both in tandem for a while.Final thoughts.The old site is really starting to fall apart. Every day I keep it open and running we steal resources from moving forward with the new site.-Any thoughts, direction, suggestions or input would be greatly appreciated

[MikeTek]

Hi Shop-Sq,

This is a tricky one to answer definitively without knowing the details of the two sites.

Having been through a very similar situation, I expect that, unless the content is truly identical, you're existing site shouldn't suffer any losses by having both live and indexed at once.

That said, until you properly redirect the old pages to their new counterparts, the new site will probably only see marginal growth. So running them side-by-side, you're not likely to get a good measure of how the new site will perform once you redirect.

In my experience, there's no way to handle a site-wide redirect like this "risk-free" with a smooth transition. But you'd have a chance to catch any technical issues that might negatively impact Google's ability to crawl/index the new site's content if you launch it well ahead of March, then set the redirects once you're comfortable (again I'd want to do this well ahead of busy season if possible). This will give Google some time to crawl the redirects, pass PageRank to the new site - and it'll give you and your team some time to work out any kinks.

Hope this helps at least somewhat - these are not easy situations to evaluate especially without detailed knowledge of both sites.

Best of Luck,
Mike