sentence1: Based on the estimated time periods needed to complete each of the four phases described above, the estimated time period to complete the implementation of ACI on one combustion unit is about 15 months, as shown in Exhibit A-5 in Appendix A. Since the permitting process limits the timeline, a faster permitting process will shorten the time necessary to install ACI on a single unit.
sentence2: the time period to complete the ACI implementation is an estimate.