Germany is seeing an explosion in companies offering e-grocery delivery in 10 to 30 minutes and their offer seems to be hitting a nerve.
Flink is reporting 3 million customers, and just started in December 2020.

Why are people embracing this service? They have been very hesitant to accept the e-grocery offers from Rewe Digital, Amazon Fresh and partly Picnic? 
Is the delivery within 10 to 30 minutes really what the consumer wants or is there something else behind the boom?
Same day or Same Hour has been hyped as the name of the (future) ecommerce game, but there could be a hidden reason for the consumers to embrace these concepts. People are fed up with having to wait for the delivery!
With instant delivery, the waiting time is practically zero. You order and within the hour the goods are there. That is why Amazon is moving their distribution centers closer to the consumer.

The pandemic showed everybody that time slots doesn’t work, and the Gorillas, Flinks and Getirs saw the opportunity and have addressed and solved that problem. So far so good.

The “Quick Ones” are having other problems. The more success they have, the more inner-city locations are required and depending on whether 10- or 30-minute delivery is promised, it will be a lot of locations and these need to be supplied by heavy trucks. Gorillas are getting a lot of flak for blocking streets with heavy trucks in the inner cities. One could expect the lawmakers to interfere and request locations where trucks may offload without blocking the streets. This makes a location a lot bigger i.e., a lot more expensive.

Another little issue is the fact that many of us go back to the office in future. This means many orders will have to be delivered in the afternoon / early evening. 
We could end up seeing a similar situation to the restaurant delivery business, which have little traffic during the week, but a lot on Sunday evening.
For the “Quick Ones” it will be little traffic during the day and a lot in the afternoon / evening. In a pure gig economy, it could work, but in more regulated countries, it could drive cost so high that the business case will never be profitable.

What can we learn from the above? That the consumer hates time slots and the uncertainty of when a delivery arrives.

Could there be another solution to the problem of time slots than instant delivery?
I believe so. Chilled food capable residential parcel boxes will make time slots redundant. One may even order without being at home for instant delivery and the goods will be delivered to your parcel box i.e. be there when you get home. 
Super convenient and will drive the last mile cost down. Fulfillment centers do not have to be in the inner city and can be bigger thereby reducing opex/capex significantly.
Residential food capable parcel boxes are win- win- win, and on top, the most sustainable last mile delivery concept.