Well this measure has both advantages and disadvantages
the main advantage is filtering out evil people. In feijea there was another solution for this problem, new citizens werent allowed to vote until they were 1 week old. anyway.. This filter is in my eyes important.
main disadvantage is, as you say, the delay is annoying for new citizens.

I'd say shortening the period is all we can do. But i wouldn't go farther than shortening it to 36 hours. one day really is not enough for most people.

having more than 3 or 4 people voting yes = automatically in isn't a good idea in my opinion.