No, unfortunately. As the landowner, your farmhands (friends) can only work on the farm if you are online in vanilla Stardew Valley. However, there is the Always On Server for Multiplayer mod that makes it so your friends can work on your farm without you needing to actively play the game or go to bed every 10 minutes. However, this mod requires that you do not close your game or minimize it - but you can open up other windows on top of your game!