Latest entry for Tier 1 visa from endorsement date

Hi Moderators and Community Contributors!

I've received endorsement letter for Tier 1 by Tech Nation on 4th Sep. However, I have a few-month-old baby, so I would not want to do the transition to UK from Singapore during the harsh winter months. I'm trying to move there as late as possible so that it is easier for baby to adapt to UK climate from the hot and humid Singapore weather.

I've done my research and found the following plan possible, and I hope to check with experts here whether my understanding of Home Office policies is correct. I know it is risky to apply so late because the endorsement letter is only valid for 3 months, but it is almost impossible for us to attempt a move during Dec-Jan winter months.

1. received endorsement letter on 4th Sep for stage 1 of Tier 1 visa application
2. apply Tier 1 stage 2 and pay NHS fees on 2nd Dec (within 3 months of endorsement letter)
3. during application, put entry date as 1st Mar (within 3 months of stage 2 application date)
4. after confirmation of stage 2, apply for wife and baby for 1st Mar entry date
5. enter the UK on 1st Mar (is it correct the latest entry is 10 days from this date?)

Thank you in advance for sharing advice!