diff --git a/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJob.cs b/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJob.cs
index 001926ba..0a20b789 100644
--- a/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJob.cs
+++ b/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJob.cs
@@ -60,7 +60,8 @@ public sealed record WorkflowJob
     public string? RunnerGroupName { get; init; }
 
     [JsonPropertyName("started_at")]
-    public string StartedAt { get; init; } = null!;
+    [JsonConverter(typeof(DateTimeOffsetConverter))]
+    public DateTimeOffset StartedAt { get; init; }
 
     [JsonPropertyName("completed_at")]
     public string? CompletedAt { get; init; }
@@ -72,5 +73,6 @@ public sealed record WorkflowJob
     public string? HeadBranch { get; init; }
 
     [JsonPropertyName("created_at")]
-    public string CreatedAt { get; init; } = null!;
+    [JsonConverter(typeof(DateTimeOffsetConverter))]
+    public DateTimeOffset CreatedAt { get; init; }
 }
diff --git a/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJobStep.cs b/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJobStep.cs
index 14b65051..e4069039 100644
--- a/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJobStep.cs
+++ b/src/Octokit.Webhooks/Models/WorkflowJobEvent/WorkflowJobStep.cs
@@ -18,7 +18,8 @@ public sealed record WorkflowJobStep
     public long Number { get; init; }
 
     [JsonPropertyName("started_at")]
-    public string StartedAt { get; init; } = null!;
+    [JsonConverter(typeof(DateTimeOffsetConverter))]
+    public DateTimeOffset StartedAt { get; init; }
 
     [JsonPropertyName("completed_at")]
     [JsonConverter(typeof(NullableDateTimeOffsetConverter))]