A program that allows employees to choose their starting and ending times, as long as they are at work during a specified core period, is called .

flextimes

Explanation:

Flex times is defined as the flexible time that is scheduled for allowing the workers to alter the workday start and their finish times. This is in contrast to the traditional work arrangements which require for the employees to start work at a standard 9 a.m. and to finish at 5 p.m.

It is program which allows the employees to choose a suitable starting time as an ending time for doing their work during the specified core period.