I started seeing improvement pretty quickly the first time I was given antibiotics (was on 30 days for a sinus infection...was surprised when it also helped my stomach). The next time I got abx (for a skin infection), it took longer to start feeling a little better. Probably because it wasn't the best kind of abx for Lyme.
I should note that I've been sick with Lyme symptoms for over 30 years, so it is likely I'll never be off of some kind of antibacterial support (abx or herbal).