Shaykh Saalih al-Fawzaan (may Allaah preserve him) said: 

The sharing that is required has to do with spending the night. So you have to divide your time between them. The same applies to maintenance, accommodation and clothing. It is essential to be fair in these matters, by giving each of them sufficient accommodation, food, drink and clothing. You must also divide your time fairly among your wives. This is the justice that is enjoined by Allaah in the verse (interpretation of the meaning):

“…then marry (other) women of your choice, two or three, or four; but if you fear that you shall not be able to deal justly (with them), then only one …”

[al-Nisa’ 4:3]

al-Muntaqa min Fataawa al-Shaykh al-Fawzaan (5/question no. 384)