When you complete the online application, you have to put an 'Intended Travel Date'.
This is the date the visa will start from (although lately they have been issuing them starting 1 week before the requested date) and he will have 30 days to enter the UK from that date (it will only be valid 30 days).
If the travel date has passed before the visa has been issued, it will be made valid for entry 30 days from the date the decision is made instead.
Once he is in the UK he will have 10 days to pick up his BRP card, which will be his actual visa, valid 33 months.
When he has the BRP he can come and go from the UK as he pleases, as long as you can show you have lived together for the entire length of the visa.
So, he could come to the UK within the 30 days, pick up the BRP and then go back to the US for a bit to sort out the house.
Note: you must either already be in the U.K., or be entering with him, when he first enters on the visa. He cannot enter before you.
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