How can I know if the epoch point is reached in seq2seq model?
It looks like there is a difference between your dev and train data:

global step 374600 learning rate 0.0069 step-time 1.92 perplexity 1.02
eval: bucket 0 perplexity 137268.32

Your training perplexity is 1.02 -- the model is basically perfect on the data it receives for training. But your dev perplexity is enormous, the model does not work at all for the dev set. How did it look in earlier epochs? I would suspect that there is some mismatch. Maybe the tokenization is different for train and dev? Maybe you loaded the wrong file? Maybe the sizes of the buckets from the original translation model are not appropriate for your dev data? It's hard to say without knowing more details.
As to when to stop: the original translation model has an infinite training loop because it has a large data-set and capacity and could continue improving for many weeks of training. But it also lowers the learning rate when it's not improving any more, so if your learning rate is very low (as it seems to be in your case), it's a clear signal you can stop.
I am training a seq2seq model since many days on a custom parallel corpus of about a million sentences with default settings for the seq2seq model.
Following is the output log which has crossed 350k steps as mentioned in the tutorial. I saw that the bucket perplexity have suddenly increased significantly the overall train perplexity is constant at 1.02 since a long time now , also the learning rate was initialized at 0.5 but now it shows about 0.007 , so the learning rate has also significantly decreased, Also the output of the system is not close to satisfactory.
How can I know if the epoch point is reached and should I stop and reconfigure settings like parameter tuning and optimizer improvements?

global step 372800 learning rate 0.0071 step-time 1.71 perplexity 1.02
  eval: bucket 0 perplexity 91819.49
  eval: bucket 1 perplexity 21392511.38
  eval: bucket 2 perplexity 16595488.15
  eval: bucket 3 perplexity 7632624.78
global step 373000 learning rate 0.0071 step-time 1.73 perplexity 1.02
  eval: bucket 0 perplexity 140295.51
  eval: bucket 1 perplexity 13456390.43
  eval: bucket 2 perplexity 7234450.24
  eval: bucket 3 perplexity 3700941.57
global step 373200 learning rate 0.0071 step-time 1.69 perplexity 1.02
  eval: bucket 0 perplexity 42996.45
  eval: bucket 1 perplexity 37690535.99
  eval: bucket 2 perplexity 12128765.09
  eval: bucket 3 perplexity 5631090.67
global step 373400 learning rate 0.0071 step-time 1.82 perplexity 1.02
  eval: bucket 0 perplexity 119885.35
  eval: bucket 1 perplexity 11166383.51
  eval: bucket 2 perplexity 27781188.86
  eval: bucket 3 perplexity 3885654.40
global step 373600 learning rate 0.0071 step-time 1.69 perplexity 1.02
  eval: bucket 0 perplexity 215824.91
  eval: bucket 1 perplexity 12709769.99
  eval: bucket 2 perplexity 6865776.55
  eval: bucket 3 perplexity 5932146.75
global step 373800 learning rate 0.0071 step-time 1.78 perplexity 1.02
  eval: bucket 0 perplexity 400927.92
  eval: bucket 1 perplexity 13383517.28
  eval: bucket 2 perplexity 19885776.58
  eval: bucket 3 perplexity 7053727.87
global step 374000 learning rate 0.0071 step-time 1.85 perplexity 1.02
  eval: bucket 0 perplexity 46706.22
  eval: bucket 1 perplexity 35772455.34
  eval: bucket 2 perplexity 8198331.56
  eval: bucket 3 perplexity 7518406.42
global step 374200 learning rate 0.0070 step-time 1.98 perplexity 1.03
  eval: bucket 0 perplexity 73865.49
  eval: bucket 1 perplexity 22784461.66
  eval: bucket 2 perplexity 6340268.76
  eval: bucket 3 perplexity 4086899.28
global step 374400 learning rate 0.0069 step-time 1.89 perplexity 1.02
  eval: bucket 0 perplexity 270132.56
  eval: bucket 1 perplexity 17088126.51
  eval: bucket 2 perplexity 15129051.30
  eval: bucket 3 perplexity 4505976.67
global step 374600 learning rate 0.0069 step-time 1.92 perplexity 1.02
  eval: bucket 0 perplexity 137268.32
  eval: bucket 1 perplexity 21451921.25
  eval: bucket 2 perplexity 13817998.56
  eval: bucket 3 perplexity 4826017.20


And when will this stop ?