When should one pursue pre-qualification and pre-approval?

[Will Graves]

I am looking to buy an investment property in Charleston, SC in ~6 months time. My girlfriend and I plan to move down there and we'd love to house hack a duplex in Charleston proper. I plan to leverage an FHA loan as an owner / occupant and put 5-10% down.

I understand the difference between pre-qualification and pre-approval for a mortgage. However, when should I begin talking to lenders to get pre-qualified? Is it too soon?

Additionally, when should I then pursue formal pre-approval?

Thanks in advance for any information and guidance!