Hi, stitches can be removed if the wound is completely healed after 10 to 14 days after the surgery. It is best checked at your veterinarian so they can check if everything is well healed before they remove the stitches. If there is a crust, some oozing, a lump, the stitches should not be removed.
Here is a link about spaying if you ever have questions about the surgery itself:
Let me know if you have more questions, or need additional information.