The playback start and end offsets are measured in ticks, and Dorico uses 480 ticks per quarter note.
To convert n milliseconds to ticks, multiply the given tempo expressed in quarter notes per minute by 0.008 and then multiply that product by n. For example, to convert 40 milliseconds to ticks at a tempo of q=100, compute 100 * 0.008 * 40 = 32.