Always use second based TimeSpan in Greenfield

BTCPayServer.Client/JsonConverters/TimeSpanJsonConverter.cs

@@ -0,0 +1,45 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using NBitcoin.JsonConverters;
+using Newtonsoft.Json;
+
+namespace BTCPayServer.Client.JsonConverters
+{
+    public class TimeSpanJsonConverter : JsonConverter
+    {
+        public override bool CanConvert(Type objectType)
+        {
+            return objectType == typeof(TimeSpan) || objectType == typeof(TimeSpan?);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            try
+            {
+                var nullable = objectType == typeof(TimeSpan?);
+                if (reader.TokenType == JsonToken.Null)
+                {
+                    if (nullable)
+                        return null;
+                    return TimeSpan.Zero;
+                }
+                if (reader.TokenType != JsonToken.Integer)
+                    throw new JsonObjectException("Invalid timespan, expected integer", reader);
+                return TimeSpan.FromSeconds((long)reader.Value);
+            }
+            catch
+            {
+                throw new JsonObjectException("Invalid locktime", reader);
+            }
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            if (value is TimeSpan s)
+            {
+                writer.WriteValue((int)s.TotalSeconds);
+            }
+        }
+    }
+}