You do not have to stay online with your account to get the profit share.
This has been such an important factor in staking ARK for me. I have tried POS coins in the past and living in a rural area internet is not 100% 24/7. With ARK vote for a delegate and the delegate takes care of the rest.
My question is with 500 Arks how many ark can I earn in a month, by voting for a delegate that shares 95 % profit rewards
Calculate it here to get a rough indication: http://calculator.reconnico.com/ It fluctuates quiet a bit based on all voter movement but good enough as a general rule of thumb.