Simply use

{{period span|'''''Period name'''''}}
Example
{{period span|Permian}}
Gives

अभिव्यक्ति त्रुटि: अज्ञात शब्द "permianround"। million years ago to २५१.९०२ million years ago

The |round= parameter will round off the number to that many decimal places. It doesn't currently round the error margins; to omit these, use {{period span/brief}}.

If this template generates an expression error, it is because the period is missing from {{next period}} or {{period start}}. Please go ahead and add it in the appropriate place (once you've checked your spelling!).

You must also add the period to {{period start error}}, which contains the errors shown after the ± in the output of this template.

Templates for retrieving data about geological periods: