Select only one radio button in a webform
The problem with the radios approach is that they're separate form fields, so the browser is correctly allowing only one selection per field.

Instead, you should use radio - https://api.drupal.org/api/drupal/developer%21topics%21forms_api_reference.html/7#radio and specify the attribute of name to only allow one value to be selected.

I'm assuming this is going to be built programmatically in a loop instead of procedurally, but I'll demonstrate as if this was hard-coded. Also, in a perfect world you'd add markup in the theme, not in the form definition.

$form['submitted']['800_title'] = array(
  '#markup' =&gt; '8 a.m.',
  '#prefix' =&gt; '&lt;div style="display:inline-block"&gt;',
);

$form['submitted']['830'] = array(
  '#type' =&gt; 'radio',
  '#value' =&gt; 'default',
  '#return_value' =&gt; '0830',
  '#title' =&gt; t('8:30am'),
  '#attributes' =&gt; array('name' =&gt; array('time')),
  '#prefix' =&gt; '',
  '#suffix' =&gt; '',
);

$form['submitted']['845'] = array(
  '#type' =&gt; 'radio',
  '#value' =&gt; 'default',
  '#return_value' =&gt; '0845',
  '#title' =&gt; t('8:45am'),
  '#attributes' =&gt; array('name' =&gt; array('time')),
  '#prefix' =&gt; '',
  '#suffix' =&gt; '&lt;/div&gt;',
);

$form['submitted']['900_title'] = array(
  '#prefix' =&gt; '&lt;div style="display:inline-block"&gt;',
  '#markup' =&gt; '9 a.m.',
);

$form['submitted']['900'] = array(
  '#type' =&gt; 'radio',
  '#value' =&gt; 'default',
  '#return_value' =&gt; '0900',
  '#title' =&gt; t('9:00am'),
  '#attributes' =&gt; array('name' =&gt; array('time')),
  '#prefix' =&gt; '',
  '#suffix' =&gt; '',
);

$form['submitted']['915'] = array(
  '#type' =&gt; 'radio',
  '#value' =&gt; 'default',
  '#return_value' =&gt; '0915',
  '#title' =&gt; t('9:15am'),
  '#attributes' =&gt; array('name' =&gt; array('time')),
  '#prefix' =&gt; '',
  '#suffix' =&gt; '&lt;/div&gt;',
);