Haven't been waiting too long.
Yeah I hear you. That is an old rule of thumb. However there are lots of things in play and raising rates currently sitting at almost zero by 1/4 or 1/2 point every year does not guarantee a market crash. Also the market has a certain amount of it factored in and is expected. Of course once the Feds announces a raise the market may still drop ... but I would be surprised if that alone 'crashes' the market by more than 20%.
The problem with going to all cash is trying to find an entry point back into the market. A good strategy is to put a little in at a time over decades spread among asset classes (including cash) and forget about it aka "lazy investor" portfolios aka coffeehouse investor. You can google if not familiar. These lazy portfolios usually beat the active professional investors ... because no one can time the market. Cheers