Hi Ram,
Is it in context of Schedule or Timezone?
1. For Schedule it would be Float day & Float week.
So consider an example of Thanksgiving [US] which is always falls on 4th Thursday of November every year where Date is not confirmed but Day & Month is & thus is schedule uses Float Day & Float Week.
So, it will be scheduled as below.
Refer link for additional check.
2. If its in timezone's context then it would simply apply the working in context to User's Timezone from User profile table. Refer link for a check.
