I will be arrive in Osaka by early morning 9am and plan to take train to Kanazawa by 5pm
If you are going to get on a local train, you don't need a pre-purchased ticket to get on. If you wish to take the express train called "Thunderbird", there seems to be two options:
- Reserved Seats (Shitei-Seki)
You can purchase in advance or on the day if there are vacancy. You will get a ticket with seat numbers (ex) 4A, 4B, etc) and the car and the seats are specified. Go to "Midori No Madoguchi", the train information in Osaka Station and you can purchase at the counter or ticket machine.
- Free Seats (Jiyu-Seki)
You can purchase in advance or on the day. Free seats does not include seat reservation, and thus, the ticket is cheaper than reserved seats, but if the train is crowded, you will have to stand all the way. But there is a possibility to get on the train even if you don't have a pre-purchased ticket. It is better to line up early to get a seat. The place to purchase the ticket is the same as above.
Express Trains or Shinkansen are usually very crowded the end of the year and new years, so it is better to purchase in advance if you can. I think it is better to purchase the ticket as soon as you arrive to Osaka.