[YMS visa] Visa start date - date of issue or expected date of entry?

Hi all, I am in the process of booking an appointment where I will be submitting my application form and biometric details. I am holding a Hong Kong passport, but have been living in the UK under Tier 4 student visa in the past couple years. I will be returning to HK for one month, do I still need to to the TB test (since Hong Kong is in the list of high-risk countries), as I have already been living in the UK?

Hi all, I have submitted the application form for Tier 5 YMS two weeks ago, where I have stated in 'date you plan to arrive in the UK' that I will be arriving 2 December 2019. However, I would like to return to the UK two weeks earlier (say 18 November 2019). Is the 30 day temporary visa valid from the date of issue of the visa, or the date that I have entered in the application form? Would it be possible to change the visa validity date when I attend the appointment/interview (I will be applying in Hong Kong)? Any costs involved? What other options do I have to arrive in the UK earlier? Thanks!