Freezing water is instantaneous
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The main argument is that the effect:
>You freeze the water, provided that there are no creatures in it.

Is instantaneous. You instantly freeze the water, then it unfreezes over time naturally. You magically froze the water. "The water unfreezes in 1 hour." isn't a magical effect, it's advice on how long the ice takes to melt. There is no lingering effect to be canceled, casting the spell again won't turn the ice back into water.

You can make an ice bridge up to 60 * 10 * 5 ft long (60 minutes per hour, 10 turns per minute, 5 ft per turn = 3000 ft

If your GM says that ice melting is magical then...
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There are two alternate options:

 - Have multiple people use Shape Water to make a longer bridge
 - Keep freezing the 5ft ahead and allow the last 5ft to unfreeze. This is less of a bridge and more of an iceberg raft.

Option 1 is easier but you need many people with shape water. Option 2 can be done alone, but your DM will probably throw some dex checks at you to stay balanced (I know I would)