Luckily this is a very common situation for people, so there is a good body of research to answer your question! A good answer is about 30 mins of moderate cardio activity a day: https://www.who.int/news-room/fact-sheets/detail/physical-ac....
"Adults aged 18–64 years should do at least 150–300 minutes of moderate-intensity aerobic physical activity;"
EDIT: Added quotes for clarity.
"->Should do ... ->Or ... Throughout the week."
Not sure why they worded it that way, maybe adults with busy schedules engage less with _ per day than _ per week recommendations.