Lemon bud to fruit, how long?

Hi,

I have a dwarf lemon shrub in my patio. The flowers have started becoming buds, but they are in that stage for last 3-4 weeks. How long does it usually take for them to grow big?
Please see the image, the buds are of that same size since last 3 weeks and I am wondering if I am supposed to do something to help them grow into fruit.





thanks,
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