Firstly, you take first element of  input_shape, and first convolution takes it as input_shape[0] which is 12. I do not know how you did set input for your model. It is depending on your design, actually. As you mentioned in your first one, 25 is time step what you want. If you did set batch size in your code, then there might been batched input.
I do not know where is the “in_channel” in your comment. However, in general, channel means that a number of input tensors operated by the convolution.
I recommend that you must check your model’s input at first. You did set batch size? You did not set batch size? If you did set so, then let you change value of batch size from 25 to other number such as 3. Then you can check input shape again by print, if it has 3 then the original 25 was batch size, but if it is not it is probably other.