We have heard that Lord Varaha rescued Bhumi Piratti from the clutches of Hiranyakshan during the deluge of waters (jalapralayam). The Lord protected the earth by holding all the worlds in his navel. Did this occur before or after creation?

The advent of srushti is called samasta-srushti. Perumal created the universe after creating the essential substance separately. During this, he created Brahamandam and then Brahma. He further created through Brahma.
This incident happened during the period between the creations. When he was creating other beings through Brahma, jalapralayam occurred. He protected the earth by killing Hiranyakshan to help Brahma in creation.