It is important that cohabitation take place at the correct times in order to ensure good health for the couple as well as their child-to-be, Allah willing.

The act of intercourse should ideally take place when there is a state of relaxation and temperamental balance in both husband and wife. Any form of tension or pressure in the form of hunger, thirst, anger, depression- illness, etc. will dampen the pleasure.

Faqih Abdul-Laith Samarqandi (Rahimahumullah) writes in his book BUSTAN that the correct time for intercourse is the latter part of the night because the stomach is full during the early part of the night and intercourse is undesirable on a full stomach. It is thus clear that intercourse is undesirable in the early hours of the night. The same has been recorded in TIBBE-NABAWI.

The author of IHYA observes that it is Makrooh to have sexual relations in the earlier part of the night because the possibility of spending the rest of the night in the state of Janabat(Ritual uncleanliness).
Hazrat Aisha (Radiyallahu-Anhum) reports that it was the noble habit of Rasulullah (Sallallahu-Alayhi-Wasallam) that after completing the witr Salah at the end of the night, he would consort with his wife if he is desire. If not, he would lay down on the musalla(prayer rug) until Hazrat Bilal (Radiyallahu-Anhum) would call out the Azaan for the Fajr Salah (Morning prayer).
It should be noted that the prohibition of sexual intercourse in the earlier part of the night is merely from a medical and health point of view. It is not a ruling of the Shariah. It is reported that Rasulullah (Sallallahu-Alayhi-Wasallam) cohabited at various times of the day and night- SHAMIAL-TIRMIZI

For those that find it inconvenient to wait for the end of the night(for whatever reason), a practical solution is to have a light meal early in the evening, perhaps before Maghrib. In this way the Stomach will not be full at the time of cohabitation in the earlier part of the night.

It is the experience of wise men that the result of sexual intercourse on a full-stomach is a dull, backward child. Furthermore, it is even harmful to the health of the male.