Welcome to the journey!
I wouldn't expect a bitter taste right after roasting that then goes away with resting (unless it's one that remains throughout the beans aging due to over-roasted beans)
But certainly, I find that the resulting brew will be smoother as mentioned as time progresses. Also the crema should settle - early on it will 'explode' out of the spout and then dissipate quickly, but will settle over a few days. I personally find 7-10 days the sweet zone. At 7 days suddenly the taste will punch through milk, and develop much more richness in a doppio. After about 14 days I find I need to start grinding coarser, as the result starts to get a bit bitter & oily due to age.
Its not that a good roast will taste bad straight out of the roaster - but like a good wine will improve with age :-)
Let us know how you get on