How do you know that your roll-out timeline is realistic and complete?

when milestones are achieved ( achievement here means time and cost ).

Rollout timeline will be realistic and complete once we can achieve planned target within target time frame without exceeding cost and following needed specifications

Hello Mr.RadiOnce we have made the Project charter we proceed to get all the key stake holders on the same page. We need to fix the timelines from all these stake holders , commercial, finance, legal, marketing,branding, other fixed vendors and make a clear chart with timelines. We must also take into consideration the time lag which can occur ,if time allows. Incase we already have a date fixed for project launch then we need to work backwards and convince all to stretch and commit a periodical meeting of cross functional members and get in HODs to meet the common company objective. Finally we need to delegate taks with timelines to the project team . And tell them that the project launch date is sacrocant and must be met.

mention every parameter in rollout tracker and get timeline, if it is overlapping then manage the timeline in a tracker. 

also, convey 2 minus timeline to your team. so no gap is come out.