Product search results

Hi,

I was searching on Google regular search box and it showed the keyword
that I was searching with some "product search results ....." in first
page.

Today I repeat the search for same keyword but it doesn't show those
"product search results ....." anymore.

1) Does anyone know why?
2) Is there a any time limits/schedule? Since, it showed me result
yesterday but not today. (To report accurately: it showed on Friday,
Saturday and Sunday but not today)

Thanks