I have definitely have experienced problems like this. Not just because the merchant interface said they would be 'searchable soon', but because product would literally not show up in Google Shopping for many hours after upload.
I think it was partially due to the size of the feed (30,000 products), and partially due to some of the products coming under extra scrutiny on each upload.
Either way, moving to uploading every 4 days did seem to help quite a bit. Only thing to keep in mind is that if you update prices on your site frequently you need to upload products to google just as frequently, the prices must match.
Yeah, that is a slight issue. We don't put prices up and down wholesale unless it is January Sale etc in which case I will upload manually asap. However, we do change maybe 1 or 2 prices every day - which adds up to perhaps 20 products a week.
I've switched to weekly since last Friday and will report back if any issues.