How much time an online shop really takes: the honest answer is that it depends on the first month
The most frequent objection from those weighing up selling online is not about cost, it is about time. And the answer has to distinguish two phases that have nothing in common.
The first phase is setup, and it concentrates almost all of the work. Company details have to be entered, shipping terms configured, the payment system connected and the products uploaded.
Uploading products is the heaviest part, and the time it takes depends almost entirely on the quality of the material you already have. If you have decent photographs and usable descriptions, it is a matter of transferring them; if you do not, they have to be produced.
One principle here saves weeks: do not upload the whole catalogue before going live. Start with the most requested products, see how they perform, and expand afterwards.
A shop with twenty well-made listings works better than one with two hundred empty ones, and it lets you open in days rather than months.
The second phase is day-to-day running, and it is far lighter than anyone who has never done it imagines.
The recurring work is essentially one thing: handling the orders that come in. When an order arrives you prepare it, ship it and update the status. It is the same work you would do for an order taken by phone, with the difference that you did not have to go out and get it.
The other recurring activities are two, and they are what separates a shop that works from one that sits still.
The first is keeping availability up to date. A catalogued product you no longer have generates an order you then have to cancel, and that is what damages a new seller's reputation most.
The second is replying. Response time to a question about a product affects conversion more than price does, because someone who gets no answer buys elsewhere without telling you.
Overall, for a catalogue of modest size, day-to-day running is measured in minutes a day plus the time to prepare shipments, which is proportional to orders and therefore to revenue.
What matters is that the load is not constant: it is high at the start and then falls. Those who give up almost always do so by looking at the cost of the first month and projecting it across the following twelve, which is the wrong way to read it.
In summary: setup and day-to-day running are two phases with very different loads, uploading products depends on the material you already have, starting with a few well-made listings is faster and more effective, the recurring work is preparing the orders that arrive, and up-to-date availability and response times are the two activities that make the difference.