140 watts is the FTP. That means you can do it for an hour, and it will be an extremely exhausting hour and you will want at least two days of rest to recover from this workout before doing it again.
If you are not chasing watts, it’s much more sustainable to do 70 watts for two hours. You can probably do this every day.
This exactly. FTP is functional threshold power, it's the maximum you can physically maintain in zone 4 heart rate for 40-60 minutes and it's physically exhausting. This is hard work, hardest work honestly. If you have gas left in the tank after you could had a higher FTP. I'll get out on the bike and do a zone 4 workout and keep a steady state of 180-200 watts through the first 20-30 minutes, by the end of the hour or hour and a half of my workout, even with breaks to break, reset heart rate, have some water, salt and glucose, I'm down to 120-150 watts at the end of the ride.
Basically, you can probably charge your macbook at peek power for an hour every other day, or every day for a short while if you're okay with burning out eventually.
Expect to need to eat 400-600 calories and a lot of water each time you do this.