Ermou Street is very vibrant at all times. Have comfortable shoes and plenty of time to walk around and do some shopping. Just have in mind that the opening times for shops are Monday to Friday from 09:00 to 21:00 and Saturdays from 10:00-18:00. On Sundays most shops are closed however souvenir shops in Plaka Area are open.
To reach Ermou street just take the metro Line 2 from Metaxourgio station towards Agios Dimitrios- for just 3 stops and get off in Syntagma Station. Alternatively take a taxi from the hotel for 10’ Hop On Hop off bus pass through Syntagma Square as well, which is a few steps from Ermou Street.