A compatible schedule is not immigration authorization. The additional work and applicable process need assessment before it is undertaken.
Identify what changed in the actual arrangement
Record the second entity, duties and proposed dates rather than assuming the first contract covers them. A general statement that both clients need consulting services is insufficient. Existing permission must be read against the real activities, employer arrangements and period.
Seasonal work in process industries generates pressure to have paperwork ready months in advance, and that pressure encourages applications built on an outline rather than an offer. State surveying licensure and any required examination usually take longer than the immigration step, and a start date built around a field season leaves no slack. TN admission is granted for a period not exceeding three years and is tied to the employment described, so an application made against an unsettled plan produces either a refusal or an authorization that no longer matches the work.