Knowing which day of the week a message will be sent on can be hard when it's set to "45 days before first day". So if you want to avoid sending messages on weekends you can choose to exclude those days for your journey with Message delivery times.
In your journey's settings you can choose which weekdays messages can sent on. These settings can be set for each individual journey and the default settings are Monday to Friday.
If a message's delivery time is supposed to be on a day that you've excluded it will be sent on the next available day instead. The time of the day is set in the message's Sent at settings.
To set your journey's send time, go to your journey and click Settings.
Scroll down the page and you'll find the Delivery times settings. Check the days you want the journey to send messages on and leave out the ones you want to exclude. Don't forget to click Save!