You may only need a line on timings. However, sometimes trusts want a short section including milestones.
The key point is to include a start date that is consistent with: the trust’s own timings; and any recruitment of staff. It typically takes three months to bring someone in from the date you advertise (time to apply, shortlist and interview; the successful candidate’s notice period with their previous employer). So, your timings need to be realistic.
Milestones are the most significant events in the timelines of the project. There’s a case for being a bit conservative: staff tend to under-estimate how long things take, and especially how long it take to get up to speed at the start of a project. At the end of the day, it’s probably out of your hands how the project is planned, but it’s no bad thing to signal to the person putting the project together that you’re okay if the work starts a bit slowly.