We got ours around 7 weeks after our PS. We did have a custom menu and a lot of custom things, like cake. Plus we ended up throwing in a lot of floral, etc.
I'd say, if you are at the past 6 week mark and you haven't heard back, just send an e-mail to your planner asking about an estimated time of arrival for your BEO, that should be enough to get you on their radar.
After we go the initial BEO we have had very minimal changes and it has been very smooth and fast.