Just let the child sleep as long as she needs to. Perhaps after 2.5-3 hours, I check on them and start making noise to wake them up naturally. Young children need lots of sleep for their developing brains.
Small children perfectly fall asleep to the monotonous sounds such as the hum of a vacuum cleaner, a hair dryer, to the sound of water or a lullaby without words.
Find the right music or sound and turn it on every time you put the baby on the bed. Only the sound should be barely audible so as not to interrupt children's sleep and not wake the falling asleep crumb.