Well there's recommendation of at least a year to fully recover and but ultimately it's whatever works for you and your family :)
Whenever feels right. I’ve friends who had their first at the same time as me but went on to have two under two. My husband and I felt ready at 18ish months, so our children’s age gap is 2.5 years. If we have a third we’ve said it would be at least 4 years so that the eldest are in school and we’d have baby time and less juggling of toddler needs. There are many considerations that each couple/family or person may (or may not) have so really it’s down to when, if ever, feels right to try for more.
We decided to try for 2nd when daughter was 15m and fell pregnant a month later so age gap is 2 yr 2 weeks but their due dates were 4 days apart
When ever they want. Most recommendations say wait a year though to give your body time to recover.