I think it will depend. If the season is a vacation season, I suspect it will have an impact. I ran mine over August, ending just after a bank holiday weekend. It was not a good time of the year in the UK to run a campaign, but I was successful in the end. I suspect holidays such as thanksgiving and christmas might not impact so much, quite a few people shop online on thanksgiving looking for black friday deals or just to have some time to browse. It would depend on marketing
In general Friday is a good day to launch, especially if it coincides with pay day. Having your campaign end just after a pay day helps as well.