I am in the final stage of my design and I am re-checking bom/components etc.
Some essential components I use (eg. HTU21D) are out of stock at LCSC. When and how will I know what the general time is for a part to be on stock?
I need the PCB completely soldered since some components are LGA and I will not be able to do that myself.
Any suggestions on how to proceed?
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
Hello ;
Normally, the quantity is updated immediately on the LCSC store system.
Share with LCSC you BOM list to find out which components are available and the delivery date for the missing ones :
https://lcsc.com/question/index.html
you can even give them a call : 0086-755-8321-0457