When picking a date and time for the celebration, you should take a few factors into consideration:
The health of the new mother and baby – Take into account the mother and baby's physical state after birth. It is very possible that the new mother will feel fine and up to 'hosting' a crowd already a few days after birth, but it is also possible that she won't feel up to this even a few weeks after. It is recommended that you hold the ceremony within 30 (or according to certain traditions, 80) days, the period in which Jewish tradition still views the woman as a 'woman who has just given birth', and which medical literature and modern psychology consider a quasi 'fourth trimester' of pregnancy.
When you will be naming the baby – If you plan to name your daughter at a public ceremony and you will be keeping the name secret until then, it would be advisable to set a date that is no later than 2-3 weeks after birth. If you didn't decide on a name during the pregnancy, make sure you leave yourselves enough time to choose a name.
Days with special significance – If you wish to have the ceremony on a day of traditional significance, you can choose one of the following days:
The first Shabbat after birth – a day on which the naming commonly takes place;
The eighth day after birth – the day on which a male infant is circumcised. This choice of day also creates a parallel to other Jewish lifecycle ceremonies, which confer special significance to the first seven days of celebration or mourning;
The fifteenth day after birth – the day on which the woman, according to Scripture, returns to society;
The thirty-first day after birth – the day on which, according to tradition, the immediate danger to the health of the newborn has passed, and on which the ceremony of the Redemption of the First Born takes place;
The first day of the new Jewish month that follows the birth – Rosh Chodesh is considered by Jewish tradition a women's festival.
There are certain days, such as Holocaust Remembrance Day, Israel's Remembrance Day for Soldiers, the days in between the 17th of Tamuz and Tisha B'av, and the days of Sefirat Haomer [counting the Omer] after Pesach, on which it is not customary to make personal celebrations because they are days of national/historical mourning. If some of your guests do not drive on Shabbat and festivals – take that into consideration as well.