be sure who ever is demonstrating the rake understands all the adjustments for the rake. First there is the tilt of the rotor. Then there is the height of the rake above the ground, then there is the PTO RPM's, (Probably should be no more than 350 or even 300 RPM's). A young teenager or new wet back can do a fair job using a roll bar rake but will tear up a rotary rake.
What a rotary rake will do for you is, fluff up the windrow better than a roll bar rake, and not build a rope.

Lets go back to basics. First drying is 75% direct sunlight on the hay it's self. Our friends in the irrigated western states are less tied to this ideal simply because their humidity is so low, the wind blows so hard and the ground is dry enough to negate most of the need of using sunlight to cure hay. For the sunshine is what a tedder is good for. It will cover 99% of the ground with hay exposing it to the direct sun. Problem comes when there is no sun. A conditioning mower will speed hay curing, but the same dynamics apply to conditioned hay as simple machine cutting. (It is my opinion I can cut with a simple cutter bar, leave the hay laying out flat and it will cure at least as quickly as conditioned hay dropped in a windrow.) You can quote me but please do not expect any references.

The other things that cures hay make up the other 25% of the inputs. Now for sure if the sun does not shine a 3 to 5 day curing time can stretch to 14 or more days. Been there done that. One solution is to bale damp hay and dry the hay with forced hot air in a hay drying barn.

Back to references there is good research to show the least cost system is to drop the hay into a windrow and bale from that windrow when cured. Every thing else adds to the expense.

When to rake, is when the humidity is above 70%. The key is humidity at the windrow, but for raking general humidity of the air will do. For baling the humidity at the windrow, at or above 70% the hay will mold, and heat. Between 70% and 65%, again at the windrow, the hay will bale up into +/- 18% moisture hay. Works for small square bales. Below 65% humidity the hay will bale in the 16% to 18% moisture range. Below 50% humidity the hay will be dry enough to shatter leaves big time. Here in CenTex I have gone to the field at 65% air humidity and the hay would still be too tough with the air's humidity down to 50%, because of a heavy morning dew. Rake the hay with the dew on it and it will be tougher even longer.

These are truths that are true world wide. Thing is we must temper our use of these truths by our local climate, and available equipment.

Something that may be of benefit is a good weather forecast. This will not change the weather but will allow us to plan. Problem is no forecaster will guarantee our hay will never be rained on using their forecast.

I assume your equipment in your climate will allow you to bale 20 acres in the time for hay to go from almost too damp to almost too dry.

Here on my first cutting, late March early April, the hay can be dropped in a full width swath and then a few hours later run a tedder. The second, cutting early May, may not need  running a tedder. The third cutting in mid June I usually cut alfalfa with a simple disk mower, as a blister beetle solution.

A light cutting will be dropped in a windrow so I can rake it but a good cutting will be full width.