Disney Sea

If I will to travel from Ikebukuro to Disney Sea, using the Yellow Line and change at Shinkiba to Miahama Station...

1 - What is the best time to start my journey if I will to avoid the office crowd?

2 - Is it advisable to go early and wait for the park to open?

Thank you.

I assume by Yellow Line you mean the Yurakucho Line.

Rather than taking that line, I recommend taking the Marunouchi Line to Tokyo Station and transferring to the JR Keiyo Line to Maihama Station.

Try to avoid the peak rush hour of 8:30 to 9:00. Since the park opens at 8:00, you could go earlier without problem.

Yellow line is the most inexpensive and averagely the fastest.

Disney Sea opens at 9:00 or 8:30 on a weekday in this December(depends on the date).
http://www.tokyodisneyresort.co.jp/tdr/japanese/plan/schedule/calendar...

Schedule and access info in English. Don't worry about rush hour during the weekends, holidays.

http://www.tokyodisneyresort.co.jp/tdr/english/plan/schedule/index.htm...

Don't travel via Tokyo Station as suggested by Jou! The transfer at Tokyo Station requires a long walk between platforms! Taking the Yurakucho Line via Shin-Kiba is the best route.

On weekdays, the rush hour is worst between 8am and 9am. If you leave before 7:30am, you should be able to avoid the worst. On weekends, there will be no morning rush hour.

Arriving early is recommended on busy days, but it is not necessary on regular weekdays.

I looked at the map and Uji is right. Thanks for pointing that out.

However, Tokyo Station is much more interesting to explore and walk through than Shin Kiba. And the Marunouchi Line train ride would be much shorter than the Yurakucho Line train ride, albeit 20 yen more expensive. So taking Yuji's suggestion might be the best. Save exploring Tokyo Station for another time. I like Tokyo Station. :)

Thank you everyone for your suggestion! Yes I mean the Yurakucho Line. Thanks again. :)