Hi Carn,

Sorry for this issue you are encountering.

This is probably a bug, and I'd recommend contacting Salesforce Support (If you haven't already).

Heres a repo I wrote using a custom object (Test__c, with a single time field, Some_Time__c). It starts with the a demo using Time as the object, then runs the same code for Test__c. The raw Time object works, and has the same syntax as the JSON, but the JSON object fails with the same message.

Time t = DateTime.now().Time(); 
String s = JSON.serialize(t); 

System.debug(s); // "13:50:40.848Z"

Time t2 = (Time)JSON.deserialize(s, Time.class);

System.debug(t2); // 13:50:40.848Z

Test__c test = new Test__c(
    Some_Time__c = DateTime.now().Time()
);

String testString = JSON.serialize(test);

System.debug(testString);
// {"attributes":{"type":"Test__c"},"Some_Time__c":"13:50:40.850Z"}
// "13:50:40.850Z"

Test__c result = (Test__c)JSON.deserialize(testString, Test__c.class);

Some additional notes from my test runs:

• Using Map<String, Object> record = (Map<String, Object>)JSON.deserializeUntyped(testString); returns a valid Time string in the map.
• Trying to access this with System.debug((Time)record.get('Some_Time__c')); fails with a:

System.TypeException: Invalid conversion from runtime type String to Time

• Since theres no Time.Parse method, I cant figure out a good way to get the string value back into a Time object

You'll probably need a custom parse method, for both the Time string & the JSON. I've written up a sample below. Keep in mind that this is a basic example and an actual parser would likely need better code to put other field values.

The custom parser does output a proper object however! You can use describes instead of field names (likely with a map of field names & types) to determine what fields are time fields & to use a special case for those fields.

Test__c test = new Test__c(
    Some_Time__c = DateTime.now().Time()
);

String testString = JSON.serialize(test);

JSONParser parser = JSON.createParser(testString);

Test__c testCustom = new Test__c(); 

while (parser.nextToken() != null) {
    if (parser.getCurrentToken() == JSONToken.FIELD_NAME) {

        System.debug(parser.getText());
        if (parser.getText() == 'Some_Time__c') {
            String label = parser.getText(); 

            parser.nextValue();

            testCustom.put(label, CustomTimeParser(parser.getText()));
        } else {
            String label = parser.getText(); 

            parser.nextValue();

            testCustom.put(label, parser.getText()); 
        }
    }
}

System.debug(testCustom);
// Test__c:{Some_Time__c=14:26:41.276Z}

public static Time CustomTimeParser(String s) {
    // 14:26:41.276Z
    List<String> values = s.replace('Z', '').split(':'); 

    // (14, 26, 41.276)         
    String hours = values[0]; 
    String minutes = values[1];

    // 41.276 -> (41, 276) 
    String seconds = values[2].split('\\.')[0];
    String milliseconds = values[2].split('\\.')[1];

    return Time.newInstance(Integer.valueOf(hours), Integer.valueOf(minutes), Integer.valueOf(seconds), Integer.valueOf(milliseconds));
}

Hope this helps.

Kindly mark this as solved if the reply was helpful.

Thanks,
Nagendra