The onset of dynamo action in planetary cores is of broad interest to understand the surface conditions and magnetic environments of young rocky planets. Previously it has been proposed that giant impacts could either help trigger dynamo action or, on the other hand, delay the onset of the dynamo. In this study we extend previous work by investigating the thermal effects of giant impacts over a wide range of planet masses, from Mercury-sized to super-Earth exoplanets. Scaling laws are developed for the core impact heating as a function of impactor and target mass, impact angle, and velocity. To estimate the time required for the mantle to remove such excess impact-heat, we develop additional scaling laws to describe the final remnant mass and core-mass fraction. Using a simple mantle cooling model, the dynamo delay times are estimated to range from essentially zero (no delay) for small Mercury-sized planets and up to $3.5$ Gyr for a giant impact onto a 2 Earth-mass exoplanet. For typical impact conditions we find a roughly quadratic relationship between dynamo delay time $Delta t$ and final planet mass $M_f$ of $Delta tsim (400~Myr)(M_f/M_E)^2$.