Batch the making, automate the sending
The reason most people cannot sustain daily posting is not writing — it is the switching cost of opening nine apps every day. Separate the two jobs completely: make content in batches when you are in the mood, and let a queue handle delivery.
An hour on Sunday can cover a week if the posting itself costs nothing.
Use a queue, not a calendar
Picking a specific datetime for every post is a small decision that you have to make dozens of times, and small repeated decisions are what actually kill a posting habit.
Set your posting times once per account, then add posts to the queue and let them fall into the next free slot. You are choosing a rhythm once rather than a timestamp every time.
Respect the ceiling
More is better until it is not. Each network has a rate above which you look automated and get quietly throttled, and that ceiling is lower than most people assume — a handful of posts a day per network, not dozens.
Volume across ten networks is how you scale without tripping any one of them.