give value to a Period Custom Field

I have a project with a Period type Custom Field "Reaction Time" and I want it to caltulate the time between the issue creation, and the time it takes to be "In Progress" State. For some reason when I give the parsed value to the Custom Field, it gets broken. Any help would be appriciated. I have the folowing code:

const entities = require('@jetbrains/youtrack-scripting-api/entities');
const dateTime = require('@jetbrains/youtrack-scripting-api/date-time');
exports.rule = entities.Issue.onChange({
title: 'Calculate_reaction_time',
guard: (ctx) => {
return ctx.issue.is("State", "In Progress") && ctx.issue.fields['Reaction Time'] == null;
},
action: (ctx) => {
console.log("now: ", Date.now());
console.log("created: ", ctx.issue.created);
let reacttime = (Date.now() - ctx.issue.created);
console.log("reacttime",reacttime);
console.log(dateTime.toPeriod(reacttime));
console.log(ctx.issue.fields['Reaction Time']);
ctx.issue.fields['Reaction Time'] = dateTime.toPeriod(reacttime);
console.log(ctx.issue.fields['Reaction Time']);
},
requirements: {
// TODO: add requirements
}
});

And here are the outputs:

now: ,1627312800465

created: ,1627045416680

267383786

PT74H16M23.786S

null

P1W4DT2H16M