I've always read that mania is more severe than hypomania. In the DSM-5 it also says something like that mania has more of an effect on daily life than hypomania (this is not the verbatim) and may lead to hospitalization. I don't think anyone is usually ever hospitalized for hypomania unless it is a serious mixed episode or involves something else like addiction, etc. I think if there is no mixed episode or other issue, then any manic episode requiring hospitalization is probably considered full blown manic.

In the DSM-5 there is a minimum number of days difference for diagnosis of hypomania vs. mania, but nothing relating to maximum days. I believe hypomania must be at least 4 days and mania must be at least a week or two (I forget exactly the length), but hypomania can indeed last weeks or months and still be hypomania.