All constitutions should try to rise just before sunrise. This will help to keep your metabolism sync with nature. For Kapha types waking up early prevents a sluggish start to the day. From sunrise onwards to about mid-morning Kapha is in its Prakopastage and needs to be reduced, or at least prevented from increasing more. The worse thing a Kapha type can do is wake up late in the morning as this keeps Kapha in an aggravated state the whole day. For Pitta types waking early will keep Pitta from accumulating to an excessive level. For Vata waking early is good because Vata goes into a reduction phase of its cycle and this is a good time for many activities.