Anyone here know how fast ACH transfers are from one account to another? Is it same day 3 business days? I'm in Canada but I can use this to build something for

Anyone here know how fast ACH transfers are from one account to another? Is it same day 3 business days? I'm in Canada but I can use this to build something for my US clients. But if it's not same or next day, I can seem my clients not wanting to use it.