Firstly, we wish to mention that vow and promise will only be considered if they were pronounced verbally; therefore, by merely thinking about vows or making intention speechlessly will not result in any ruling whatsoever with regards to vows and promises.
In the enquired scenario, the person will feed the needy or give the Sadqat ul Fitr amount to the needy as soon as possible for all the vows he had taken, since his vows were fulfilled.
Moreover, if he intended a specific number (1, 2, 5, etc.) of needy people, that specific number of people should be fed with an amount of Sadaquat ul Fitr each. However, if he only made an intention to feed needy people (without any specific figure) when he made his promise, he will be obliged to feed 10 needy people or give 10 needy people the amount of Sadqat ul Fitr.i