there was no specific information available about Timothy Olyphant fulfilling a childhood dream while working on "The Mandalorian." However, it's worth noting that Timothy Olyphant did join the cast of "The Mandalorian" in its second season, playing the character Cobb Vanth, the marshal of Mos Pelgo on the desert planet Tatooine. He appeared in the first episode of the second season titled "Chapter 9: The Marshal."
Without further updates, I cannot provide any specific details about any childhood dream he may have fulfilled while working on the show. It's possible that new information has emerged since then. I recommend checking more recent sources to get the latest updates on Timothy Olyphant and his experiences on "The Mandalorian."