in filters, there seems to be no easy way to partially clear dates.
for example, you have some quite complicated filter, and you'd like to remove starting or ending date. this can't be done without completely recreating the filter, as deleting the values replaces them with zeroes that zabbix doesn't like afterwards.
it should be possible to easily clear partial date conditions, either by allowing to manually clear the fields (and not inserting those zeroes), or adding 'clear starting/ending date' after the calendar buttons.