I recv'd an email from our travel agent, and there was a slight change to our ferry schedule, resulting in an unplanned stop in Sifnos before moving on to Milos.

We will have from 12:35 to 14:00 - will we have time to do anything such as get a bite? I should tell you we will be going back to Sifnos three days later to spend a few days so I can explore more in depth then.

Is there a good place to grab a bite near the ferry?

There are excellent restaurants in the port, Kamares: we ALWAYS eat at the very first one you come to as you leave the ferry. It's called Poseidonas: it has a very extensive menu: I can recommend the traditional chickpea croquettes and meat casseroles - the goat in lemon sauce is particularly delicious! Excellent fish, too: I had red mullet there TODAY! You can sit by the water and enjoy the view of the mountains. When you come back to Sifnos, try to have a meal at Argyris' taverna on the opposite side of the harbour - it's particularly good at sunset, when there's a wonderful view of Kamares across the water and the mountains behind. Great grills in the evening, too!

Thanks for the suggestions Nikoletta. Do you think we will have time for a lunch if we have only 1 1/2 hours?

Greek ferries don't run to precise schedules like railway trains. The weather and all kinds of factors can make a difference: some ships will be more punctual than others. Nobody on this forum can predict what the weather might be like on Sifnos.
Why not just take things as they come? You may have time for a quick drink or a snack or a meal. Visiting the Greek islands can be great fun, but you cannot plan a fixed schedule.

Point well taken.

Actually, though, the boats, especially the highspeed ferries on the Piraeus, Sifnos, Milos route are usually very punctual - unless it's one of the G and A ferries, which are not so reliable - but they usually come in the evening. You should have plenty of time: you can leave your luggage in the covered waiting area, so you won't have to lug it about with you, but the restaurants and shops are close to the ferry. Most of the food will be ready, and things like grilled fish don't take long - you can always tell them you're catching the boat. It should be a nice, relaxing intro to Sifnos before you come back!