Hi All, I got my stage 2 approval so wanted to share my updated timeline:
Aug 17 2020: Submitted stage 1 application
Aug 21 2020: Received Tech Nation endorsement letter
Nov 12 2020: Submitted stage 2 application, booked biometric appointment
Dec 18 2020: Submitted biometrics
Dec 28 2020: Received passport with approved visa (90 day vignette)
I received a 90 day vignette in my passport that’s valid till April 2021. The start date on the vignette is the intended date of travel that I wrote on my stage 2 application. My passport & vignette came with a letter that says:
"Your passport/travel document contains a vignette (visa sticker), which you will use to travel to the UK. The vignette is valid for 90 days. If you do not arrive in the UK within this 90 day period you will need to apply for a vignette transfer, the fee for which can be found at www.gov.uk/visa-fees
What you must do after arrival in the UK:
Details of your permission will be on your BRP. You must collect your BRP from the following collection point before your vignette expires or within 10 days of arriving in the UK, whichever is the later. If you are required to quarantine in line with government guidance, please do not visit your collection point until after your quarantine period has expired. If this takes you beyond your vignette expiry date, your BRP will be held at you collection point for 90 days from the start date on your vignette and will be available for collection once you are able to collect."
To answer my original question, it seems that as long as the stage 2 application is submitted within 3 months of receiving the endorsement letter, it should be fine (even if biometric appointment is late).
Hope this is info useful for others. Thanks to everyone for your help!