I was a founder of a company in the TS Chicago class this summer.

I can tell you that this letter of intent was one and a half pages long, contained a simple, bulleted list of documents required for due diligence, and explained the structure of the funding and program.

Additionally, there is a very clear line that indicates that they are willing to extend the deadline provided you give a reason.

Finally, this document is not the formal acceptance of anything related to the program.

I would suggest that "demand[ing] it back" using "high pressure sales techniques" is a strong overstatement.