You cannot schedule more than one Flex Daily schedule for any given zone(s). Flex Daily needs to know what will be applied. Although you CAN schedule another schedule type, like Fixed, to the same zone(s) and Flex Daily will know about that water being applied and consider it to decide when to water.
Using Fixed schedules you could do what you’re asking (one schedule start at one time on one day, and another start at a different time on another day). You’re taking responsibility for how much water is being applied, though.