If you write down the ideal times you’d like to do the trips, you’ll be able to know exactly what you’re aiming for when you go to book.
If you are hoping for a hiking trip on a long weekend, or hoping to do a well trafficked trail in the middle of the most popular time of year, you’ll have way more competition for backcountry reservations.
If you’ve been really aching to do one specific backpacking trip, then plan it on a range of weekdays when you are more likely to get availability- if you can book outside of weekends, you’ll have way more opportunity to get the trips you really want to go on.
If the only time you have available is considered a “hot” time (most weekends during the summer months, and especially long weekends and holidays), figure out when reservations are opening, and be ready to be on the phone or online as soon as it happens.