Use Fieldset Legend with bootstrap

That's because Bootstrap by default sets the width of the legend element to 100%. You can fix this by changing your legend.scheduler-border to also use:

legend.scheduler-border {
    width:inherit; /* Or auto */
    padding:0 10px; /* To give a bit of padding on the left and right */
    border-bottom:none;
}

JSFiddle example.

You'll also need to ensure your custom stylesheet is being added after Bootstrap to prevent Bootstrap overriding your styling - although your styles here should have higher specificity.

You may also want to add margin-bottom:0; to it as well to reduce the gap between the legend and the divider.

I had a different approach , used bootstrap panel to show it little more rich. Just to help someone and improve the answer.

.text-on-pannel {
  background: #fff none repeat scroll 0 0;
  height: auto;
  margin-left: 20px;
  padding: 3px 5px;
  position: absolute;
  margin-top: -47px;
  border: 1px solid #337ab7;
  border-radius: 8px;
}

.panel {
  /* for text on pannel */
  margin-top: 27px !important;
}

.panel-body {
  padding-top: 30px !important;
}

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<div class="container">
  <div class="panel panel-primary">
    <div class="panel-body">
      <h3 class="text-on-pannel text-primary"><strong class="text-uppercase"> Title </strong></h3>
      <p> Your Code </p>
    </div>
  </div>
  <div>

This will give below look.

Note: We need to change the styles in order to use different header size.

In bootstrap 4 it is much easier to have a border on the fieldset that blends with the legend. You don't need custom css to achieve it, it can be done like this:

<fieldset class="border p-2">
   <legend  class="w-auto">Your Legend</legend>
</fieldset>

which looks like this:

I had this problem and I solved with this way:

fieldset.scheduler-border {
    border: solid 1px #DDD !important;
    padding: 0 10px 10px 10px;
    border-bottom: none;
}

legend.scheduler-border {
    width: auto !important;
    border: none;
    font-size: 14px;
}