It has become accepted knowledge that the planet Earth was birthed via a swirling cloud of dust and gravel clumping into larger and larger pieces of rock. It began 4.54 billion years ago, and 100 million years later, the newly molten Earth was 8,000 miles wide and 25,000 miles around.
But in this alternate universe, Earth was birthed five billion years ago, as the gravitational pull of the newly birthed sun lured in wandering dwarf planets from neighboring star systems. The result is that dozens if not hundreds of dwarf planets (varying in size from that of Ceres, 945 kilometers wide, to that of Ganymede, 5268 kilometers wide) crashed and merged together to form newer, larger bodies before becoming planets. Their surface and core compositions would vary from rock to metal to ice.
This alternate Earth was formed from such collisions before Theia arrived to make an even bigger crash. Back home, it took Earth 100 million years to reach its modern size, and that was from asteroidal clumping. In regards to the speed in which to reach full size, would it make any difference if Earth was instead formed from the colliding and re-merging of wandering dwarf planets captured by the gravitational strength of the sun?