I noticed that when trying to update a SharePoint list item using a CAML query from an InfoPath form, if the date/time format was not correct the field in the SharePoint list item would not be updated. Any updates in the CAML query after an element with an invalid date/time format were also not applied.
The Date Time format in a CAML query must comply with the ISO 8601 standard. This means that to update the time component of a Date/Time field in a SHarePoint list, the time and date must be formatted according to the ISO 8601 profile.