Once Odin died in the Marvel Cinematic Universe Thanos personally started collecting the stones. Does that mean he was no match for Odin? Or was it just right timing?
Was Odin the reason Thanos never collected the stones personally?
Not really, no. Thanos' hunt for Infinity Stones has started in 2012 in The Avengers. Remember, Thanos sends Loki to get Tessaract (i.e. Space Stone) by giving a scepter that contained the Mind Stone. Eventually, Loki gets defeated and the Tessaract was kept in Asgard's vault.
In the post-credits of Avengers: Age of Ultron, Thanos is shown saying,
Fine. I'll do it myself.
So, he was tired of failure of whoever he sends to retrieve Infinity Stones. Therefore, he decided to collect them by himself.
Moreover, it is not stated in movies nor there are official words till now regarding if Thanos is no match for Odin. We haven't seen them fighting each other. Neither it is stated that he was only waiting for certain people to die before starting collecting them. You will find many fan theories, but there is no official words regarding this.
Or just it was right timing?
So, it was just a coincidence.
Thanos' motivation to start collecting the Infinity Stones himself, as shown at the end of Avengers: Age of Ultron, is that he's grown tired of his subordinates' failures to collect them:
THANOS: Fine, I'll do it myself.
The fact that Odin happened to die at around that time is sheer coincidence. I don't believe there's any indication in the MCU that Thanos even knows who Odin is, let alone that he was hanging back out of fear of Odin.