This is a parser for source engine save files which creates an in-memory representation during parsing. It is currently a super duper work in progress and only explicitly supports Portal 1 (although it does seem to work with Portal 2 👀). Here's an example of how you could use this to get the time of a save file:

SourceSave save = new SourceSave("your favorite save file.sav");
save.Parse();
// get the server state file (there might be many (don't ask))
SaveGameStateFile sFile = save.StateFiles.OfType<SaveGameStateFile>().First();
// get the appropriate field from the "header"
Time t = sFile.SaveHeader.GetFieldOrDefault<Time>("time__USE_VCR_MODE");  // just use "time" for p2 saves
Console.WriteLine(t);

35.864998

In general, there's lots of juicy stuff in a save file and it's not necessarily the most easy thing to find what you need. The best way to find a specific thing that you're looking for is to do a verbose dump of the parsed data to a text file and ctrl+f your way through that and then struggle to figure out how to get it from the code later.

using var w = new IndentedTextWriter(new FileStream("your favorite file.txt", FileMode.Create));
save.AppendToWriter(w);

This will create a fully readable text representation of the parsed data (note that there's still lots of stuff that isn't parsed yet). A sample of this verbose dump can be found here.

A save file is actually composed of multiple files which have .hl1, .hl2, and .hl3 extensions; usually there is just one of each. So far, this project has been focused around parsing the .hl1 files, which seems to contain the server-side state of the game. I believe .hl2 files contain the client-state state and most (all?) of the time the .hl3 file is empty.

In game, the vast majority of the data is written and read with datamaps. A datamap contains a list of fields in a class/struct, each of which is represented with a type description. The type description has the name of the field, some additional flags, (which I don't use atm) how many elements there are (it can represent an array), and the data type of the field (or a custom read/write function). I tried to copy this process closely (as much as seemed reasonable in C# anyway). There are several classes that inherit from the DataMapGenerator class which contain the instructions for creating many datamaps (this is done during run time before parsing). During parsing, each parsed field is stored as a ParsedSaveField object, each parsed map is stored as a ParsedDataMap object, and each parsed .hl file is stored as a EmbeddedStateFile object.