Does the number of entrants matter? Should I favor posting longer giveaways?

Not in that regard, no. As you point out, you'll only end up with a larger number of entries. Whether you want that or not is up to you.

Length of your giveaways matters only if you want to give more people a chance, mostly because timezones.
Other than that, no real difference for you as a GA creator if 100 or 1000 people enter your giveaway.

As a publisher or promoter for something, you'll want to reach a lot of people, so a longer running time can be preferred. I personally prefer entering and giving out games with smaller crowds, so I rarely do public giveaways, instead I solve and make puzzles, where there's bound to be less competition.

It doesn't count toward anything, but I personally like giving more people a chance to win. It's one of the reasons why my whitelist is so big (compared to most) and why almost all my public- and forum-GAs (aka invite-only ones) are Level 0. With that said, giving to groups (where there are so many generous people) also has in important place, and there the number of entries is always going to be relatively small.

I just like to give chance for people who are intrested in the game, and not for the ones who are at computer at that time - so I rarely make shorter giveaways than a day, usually rather two. But technically no difference, 6 people gives just as much CV as 6k

When you create longer giveaway, people who have that game wishlisted will probably see it. Otherwise for shorter giveaways it's more likely to be won by someone who doesn't want it that much.

public ga gives cv with 1 entry.
invite-only /whitelist /group needs at least 5.

>Does the number of entrants matter?
No
>Should I favor posting longer giveaways?
Favor what you favor, it's purely to your personal tastes.

>I know you must have more than 5 people enter, but is there a difference between posting for an hour or a day?
The longer a giveaway lasts, the more entries it gets.

>Does it matter if 1000 people would enter or 100?
Generally, the lower entries, the more excited the people involved will be over it.
The shorter a giveaway, the lower the entries.
Hence 'flash giveaways' are often responded to very positively.

Flip side, if you're doing low-level public giveaways, there's a fair chance of getting cheats and exploiters and leeches winning your gibs- and they're more likely to enter low entry giveaways, regardless of if they want the game or not.
Longer giveaway lengths, of course, mean more people have a shot at the win, as well.

Basically, if it's a game you want to see go to someone 'worthy', post a private giveaway link on the forums (for better filtering, use the sgtools filter or add prerequisites to you giving people the link, such as an itssohard puzzle), or use a high sg contributor level limitation.

Comparatively, giveaway duration is a minor element in determining the results of who wins a giveaway.

I like making giveaways for 1 hour. That way less people will be disappointed at missing out. In either case, there will be only 1 winner who will be happy, with shorter duration, there are less that are unhappy.

if you have non bundled games or popular bundled games, you can even make flash 1 hours GA's up to level 9 and still easily get at least 5 entrants.

better chances at whitelist and group invites, faster point earnings (high level members tend to marked received very quickly as they know ho wit feels only too well what it feels like to wait)

level 10 takes a little longer just because of the fewer numbers of them.

Based on my experiences, there are many factors, yet one thing seems to be valid every time: the majority of the entries are made on the first hour (when it is fairly high on the New tab) and the last (when it gets closer to the main page). The only exceptions are the feature (50+ copy) GAs, which receive a constant rate since they are always in front of the people.