Extract dates in a period

I need to extract the first and the last dates of a period to use to filter the values of a lookup table containing a list of dates. I have to do this because, in addition to the Timestamp, I have to search events also by indextime, putting these dates in a dropdown list, but I cannot load the list at search time because there are too many events, so I loaded the list in a lookup (updated every night) but in my forms I have to correlate this list to the Time period. I cannot use head and tail commands because I heve too many events (head command is fast but tail is very slow!) Is it possible to extract dates from the earliest and latest values? Thank you. Giuseppe