how to allow delay in looped http request but also use Promise.all to detect when requests are done

Hi I am trying to allow 50ms before next http request is made to the server but also would like to implement some function when all the request have been made.

I made an example to illustrate what I would like to do.

So below is my example express api

app.get('/morans/test', (req, res) => {
    console.log(`start test request`);
    let targetUrl = `http://vb-dev.bio.ic.ac.uk:7997/solr/genea_expression/smplGeoclust?q=text:"GO:0003674"&stats.facet=geohash_3&rows=10320`;
    let i = 0;
    let promises = [];

    console.log(`making request ${i}`);


    for (let i = 0; i < 200; i++) {
        setTimeout(
            () => {
                let testReq = new Promise((resolve, reject) => {
                    http.get(targetUrl, (result) => {
                        result.on('data', (chunk) => {
                            console.log(`working ${i}`);
                        }).on('end', () => {
                            console.log(`ending ${i}`);
                        }).on('error', (err) => {
                            console.log(`this is error message ${err}`);
                        })
                    })
                });

                promises.push(testReq);
            }, 50 * i
        )
    }
    Promise.all(promises).then(() => {
        console.log(`done`);
    });
});

The delay works fine; however, Promise.all(promises)... is getting a premature trigger (console.log('done') triggers as soon as first request is made). It works fine when there is no timeout so I am thinking that the setTimeout is not allowing enough time for promise to be pushed to promises array. How can I write a code so that http request is made in every 50ms but also know when all the requests are successfully returned?

via serendipity