Dynamic Linq custom type conversion for query

Question

I'm trying to use dynamic Linq (System.Linq.Dynamic.Core) to query data from MongoDB, based on a SQL-like string query I get from Excel. This works, but I'm trying to change the semantics of date - long comparisons.

I'm trying to enable queries where I compare an ISODate field with a double representing the Excel datetime (OLE automation date, number of days since 1899-12-30), but any parsed long gets cast into a DateTime based on the number of 100ns intervals since 0001-01-01T00:00.000 Gregorian via this overload of the datetime constructor.

I want to somehow change this, so that an integer/double in a comparison gets cast into a DateTime for comparison via the DateTime.FromOADate(Double) function.

The official MongoDB driver supports the IQueryable interface, and I'm using it directly.

Here's the base for what I'm trying to accomplish:

MongoClientSettings settings =
MongoClientSettings.FromConnectionString(
 "mongodb://my-mongo.local"
);
settings.LinqProvider = LinqProvider.V2;
MongoClient client = new MongoClient(settings);

var database = client.GetDatabase("my_db");
var collection = database.GetCollection<BsonDocument>("colls.my_coll");

/* colls.my_colls consists of members like this:
{
 "_id" : ObjectID,
 "name": string,
 "numeric": double,
 "date": ISODate
}
*/

// in the query, 44920 is the OLE automation date representation of
2022-12-25
var results = collection
 .AsQueryable<BsonDocument>()
 .AsQueryable()
 .Where("date < 44920 and name != \"badname\" and numeric >= 520");

This doesn't work because the integer gets interpreted in the 'wrong' way.

One potential solution that came to my mind was to map the MongoDB result to a custom class, and use a custom (DateTime- wrapping) class for the date field in it, which has the proper conversion constructor for int/double. I would then have to use a custom TypeConvertor to implement an automatic conversion (I found this in the tests), but I don't fully understand how TypeConvertors work (I'm a recent C++ to C# convert).

Am I on the right track? Am I missing something? Is there a better way?