Try some of below - the poller settings are separate, but important part is timeBetweenTransactions and afterConnextionDelay defined at the connection level.
Its important to note that SDongle is able to handle just one TCP connection at the time (at least it was case 3 years ago).
UID: modbus:tcp:huawei_1
label: Huawei 1
thingTypeUID: modbus:tcp
configuration:
timeBetweenTransactionsMillis: "250"
port: "502"
timeBetweenReconnectMillis: "10000"
host: ….
connectTimeoutMillis: "10000"
afterConnectionDelayMillis: "2000" # new parameter available in OH 3.3
id: "1"
enableDiscovery: "false"
Background of below settings comes from below post, you may consoder checking entire topic for further tips: Reading data from Huawei inverter SUN 2000 (3KTL-10KTL) via modbus TCP and RTU - #118 by splatch