Can lust be developed or is it essential to instantly have that attraction?

It works both ways.

You can feel instant lust for someone (which could possibly disappear when you get to know them better)

Just the same as it can develep (as you get to know someone and realize you really really like them!)

Although, I think if you find someone personally repulsive for whatever reason instantly, that lust will never develop regardless of how much you like them.

it's usually instant for me but I have found sometimes it does develop. I'll look at someone in a different light for no real reason.

it can be developed.
When we were dating, I was more attracted to (my now husband )him "spiritually" than anything. He was just physically different than I was used to wanting; in almost every way. The personality fit felt really good, but afa being really in lust with him, that was not really there, and I am a very sexually motivated woman. Sex is paramount to just about everything in a relationship to me. I asked God that if this man was the one that was right for me, and we were going to get married, for Him to make me more attracted to Him. Once we were married I asked HIm to inspire more feelings of attraction for my husband... that He would inspire a "holy lust" in our hearts for one another . Now I can't get enough of him! So, yeah. but we have to want to want it.

I think the younger you are the more instant it has to be and as you grow older you begin to learn that everyone has something beautiful about them and looks disappear over time anyway.

Sometimes lust can grow when you become very close to a good friend and start to see them in a different way. That happened to me once before. Most of the time lust has to be instant, though, or you end up with a warm friendship with no real physical chemistry.

It can develop over time, but I don't think it can be forced. For me, when it's not instant, it develops in ways that I don't expect.