The liver and muscles can store enough glycogen for about 2.5 straight hours of aerobic activity. So not so much a casual walk, but more of a power hike.
I’d recommend hydrating with water and electrolytes the night before, waking up early and going for a long walk. Let your body show you how long it wants to go and set aside the mental voices that rationalize why you should stop. Call it your ketosis walk.
You may not get to 150-minutes, but just go and try and surprise yourself. Ask yourself, can I go another 5 minutes? And if the answer is yes, do it.
Then, afterwards, make some bulletproof coffee. The aerobic activity will sensitize you to nutritional intake. Your body will be asking. If you answer its “Ask” with fat, it will respond by saying “oh, so I get energy from this?”
After drinking your bulletproof drink (tea, coffee, a shot of olive oil or whatever fat is palatable), set a timer for 30 minutes. You might be hangry or have pangs, but let that 30 minutes pass. Then when the alarm goes off, ask yourself, am I full enough to wait a while to eat? Hopefully the answer is yes. If no eat a zero carb meal such as eggs and bacon cooked in lots of fat and then putting slices of butter on top of the eggs afterwards.
Then set an alarm for 30 minutes and at the end of it ask yourself if you are full.
Then plan a dinner that sounds appealing to you with 20g or less of net carbs. Maybe an affordable slice of meat and a salad with high fat dressing.
Track everything for the day, despite it perhaps being a pain in the butt. It will be reassuring to see macros of 5% carb, 15-20% protein, 75-80% fat. Keep your deficits/surplus ± 500 calories so as not to stress your system.
Hope some or all of this helps.