Two flights a day, once a week is perfectly fine if that works for you. In my experience, pretty much every student can cope with 2 lessons, where they have a break in between.
Broadly speaking, the more frequently you fly, the better progress you will make, as you have the benefit of more continuity and recency.
As to what time of day is best, just do what suits you best and accept that the weather will force some of the lessons to be cancelled. There are plenty of things to do within the process of learning to fly, that don't actually involve going flying, so even bad weather times can be utilised.