We use unbounce pages with forms to capture lead details.
We have 2 separate sites which convert well (25%+) in the morning and late afternoon and evening but do not convert at all between 2-4pm (GMT) despite still attracting targeted clicks in Google Adwords.
We know the industries and know that other sites (not using unbounce) do convert steadily across all hours.
Could there be an issue with Unbounce page loading? (calling external javascript for example) that only occurs at these times