Organize repeating timestamped values in schema
I'd go with the 2nd approach.
Don't be afraid of Join(t)s.
Here are some reasons


Fast enough. Chances are extremly low that you'd rely on the additional speed you gain from a flat structure, if there is any. It's not worth such an ugly hacky design
More flexible. You can add a 5th timeframe per value later and don't end up with empty columns
Less redundancy. (see following paragraph)


You should consider taking the Value names and addition value
   properties (unit, measurement device, measurement method, etc.) into
   a 3rd table and link both it with main model over the timeframe and
   the value.
This is because the value name is a relatively huge string that is stored for every timeframe. Storing only a 4 byte integer (FK) is more efficient and flexible.