It looks like you left off the ending of your sentence.
SEO is a 24x7 campaign. If you're looking to target specific days, you'd want to take advantage of PPC, SEM and Banners (or forum postings etc - if people are reading on the weekends).
You'll notice even here on HostingDiscussion, the weekends are generally a lot slower for postings than during the week.
People looking for backups on the weekend are definitely possible, and a hosting company should operate 24x7 in order to accommodate those needs however usually, you'll find many hosting companies run a skeleton crew for online purchase sales on a weekend, if any.
Some real world numbers;
Tuesday 14th: 70 tickets
Wednesday 15th: 102 tickets
Thursday 16th: 102 tickets
Friday 17th: 58 tickets
Saturday 18th: 27 tickets
Sunday 19th: 34 tickets
Saturday 11th: 33 tickets
Sunday 12th: 26 tickets
So, for us, and for most hosting companies, the weekends are generally slower. That doesn't have much to do with the marketing being done, it has to do with the clients or target market.
Some people confuse SEO with Marketing. They're not the same. SEO is PART of marketing, but should never be the only marketing strategy of a company.