The time it takes to warm up a dedicated sending domain varies for each sender. Depending your list size, it can take up to 30 days to fully warm your dedicated sending domain. When you first set up a dedicated sending domain, it is recommended that you just have the high engagement flows (welcome series, abandoned cart, and browse abandonment) running for a few days. Once you are ready to send your first campaign, make sure you send to a highly engaged segment and aim for 30% in open rates. Afterwards, the subsequent sends should strive for 20%+ open rates.
For additional resources on how to warm up your sending domain, you can check out the Guide to Warming Your Sending Infrastructure article.