First, check what your week really looks like
Look at the next few days and mark fixed commitments, commuting and times already taken up by work or caring responsibilities. Find one realistic opportunity for activity, not an ideal block of time that rarely happens in practice. Your abilities and the time you need depend on the activity you choose.
If you plan to be active with another adult, agree in advance when each of you will have time for yourself. It is easier to include an agreed time in a shared schedule than to look for a free moment at the last minute.
Reduce the time you need to get ready
Choose a place that is easy to reach or an activity you can do close to home. Prepare your equipment and clothes in advance. Fewer extra decisions make it easier to start when your time slot is short.
Choose a specific time and put it in your calendar. If the time depends on work or other commitments, choose an alternative day or time as well.
Have a shorter option for days that change
A full session does not have to be your only option. Before the week begins, decide what you will do if you have less time: choose a shorter option planned in advance or move the activity to the next realistic time. In the A/B/C/D system, Plan B is your regular, full session. Plan A adds something planned in advance to Plan B, Plan C is a shorter version, and Plan D is the smallest safe step.
You do not need to exercise every day or make up what did not fit into your plan. Rest is a valid choice when you need it; Plan D does not replace recovery.
Check what works in your life
After a week, check which times were realistic and which ones regularly fell through. Change the time or place, or prepare a simpler option. Your schedule does not need to be perfect; the important thing is to adapt your plan without giving up on all activity.
Also read how to fit activity around work and everyday life and how to plan your own activity. If you want to focus on keeping a rhythm, read how to stay consistent with training.