The 30 days applies to all federal employees, unless some stricter rule applies, so any staffing reductions because of the sequester won't start to take effect until later in March at the earliest.

Keep in mind that even then it may not happen immediately. Each agency can come up with a plan for reductions of spending. Some may choose to delay furloughs until later in the year, because only some may be necessary. Others may "spread the pain" over the entire period.