have （no/a lot of) time to do sth中，不定式为time的定语，不定式的动作还没有发生。have a tough time (in) doing sth中，现在分词作方面状语或时间状语，在做某事方面或过程中经历了一段困难时期。等于 have difficulty (in) doing sth. 介词in可有可无。有in则doing为动名词，介词短语作方面或时间状语。He used to have to look after his younger brother. to have为不定式。
