may be a normal interval for ICO three to four months. Or even six months.

Six months is normal period for ICO, but the first 3-5 months must be used for preparation to heat up the audience, and then the client is warm - it`s time for tokensale
Token sale itself should not be too long, because people can hold their money till the end. That`s why pre-sale price is lower than those at the end, and generally token sale last not more than a month..
But here we have another case, the audience is just beginning to warm, but the prospective is good enough to prolong ICO for a week or two.
Not much time left for us to know what will be in fact
Yes! There is no need for a 3 month long Tokensale, all the ICOs which are having such sales are doing it for just trying to scam more.
Look at all the high class ICO they don't need any kind of long periods! They even need whitelisting for selling all the tokens!