In India, especially during summers, there is a general trend to sleep during the afternoon. Bhai Sahib Randhir Singh jee used to advise his working companions to get a little sleep after Amritvela and before going to work.
If you can get 4 hours sleep at night and then get up at Amritvela (around 1am - 2am) , followed by a quick nap of an hour or so (after Amritvela), you would be fine. At the most, you may want to get an extra hour or two nap, after 4-5 days (weekends). This is provided you do Paath and good Amritvela.
8 hours straight sleep is definitely a myth for Gursikhs.
Kulbir Singh
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥