The delegation is working due to the NS records you have added to Cloudflare but you can’t resolve the NS (or other) records as those AWS nameservers aren’t resolving for your subdomain yet.
dig +trace +nodnssec aws-dev.timetopet.com
; <<>> DiG 9.10.6 <<>> +trace +nodnssec aws-dev.timetopet.com
;; global options: +cmd
. 513584 IN NS a.root-servers.net.
....
. 513584 IN NS m.root-servers.net.
;; Received 239 bytes from 127.0.2.2#53(127.0.2.2) in 28 ms
com. 172800 IN NS a.gtld-servers.net.
....
com. 172800 IN NS m.gtld-servers.net.
;; Received 846 bytes from 2801:1b8:10::b#53(b.root-servers.net) in 107 ms
timetopet.com. 172800 IN NS paul.ns.cloudflare.com.
timetopet.com. 172800 IN NS uma.ns.cloudflare.com.
;; Received 365 bytes from 192.54.112.30#53(h.gtld-servers.net) in 32 ms
aws-dev.timetopet.com. 300 IN NS ns-1473.awsdns-56.org.
aws-dev.timetopet.com. 300 IN NS ns-16.awsdns-02.com.
aws-dev.timetopet.com. 300 IN NS ns-1844.awsdns-38.co.uk.
aws-dev.timetopet.com. 300 IN NS ns-908.awsdns-49.net.
;; Received 186 bytes from 173.245.59.135#53(paul.ns.cloudflare.com) in 20 ms
;; Received 39 bytes from 2600:9000:5307:3400::1#53(ns-1844.awsdns-38.co.uk) in 28 ms