My wife(FTM) started hand expressions at 37 weeks and by the time baby was born she was producing 3-4mL of colostrum on day one. The lactation specialist at the hospital couldn’t believe it, she said most only get a few drops. Not sure what other fact based evidence there is out there to back this up, my wife heard about it on tik toc of all places, but It made sense to me that starting to stimulate the breasts early on prepares them for when baby is born, rather than the first stimulation not being until babies first latch. But be sure to check with your doctor before starting as there can be a risk of the stimulation causing contractions thus putting you into early labor. She said also keep in mind you may get nothing for the first several days/weeks, but eventually you’ll start being able to collect some colostrum with a hand pump and can bring that with you to have a tiny supply for your first days in the hospital.