options theta and holidays

#1
Dear traderji members,
Can you please tell me that whether options theta is calculated on daily basis or hourly basis? Buying an option will lose value with time but is that calculated on daily basis? Another very important thing is whether options lose value also on holidays? If they do, then that means it is never a good idea to buy an option on a friday(in general)? Please clarify if possible

.............................Suvadip Ray.................................
 
#2
dear suvadipji,

As i understand theta is a measure of derivatives value (erosion) with respect to time. So nearer the expiry the the lower the value goes. I also hold your views on theta. (eventhough the effects i believe is minimal)