> Isn't the problem with that that investors expect that their capital be deployed immediately, and if you can't do that they aren't interested?

That strongly depends on the investors. The vast majority is perfectly content with a spending schedule that runs over one or more years.

My (limited) experience is less about the immediacy of use, but more the expected return and valuation it establishes. A 'too-high' valuation would likely make things more difficult in the future if expectations aren't met/exceeded.

rule of thumb the money of a round is to spent 1 to 2 years.