--- main.cpp ---
#include <QCoreApplication>
#include "a.h"

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    QElapsedTimer timer;
    timer.start();
    A a;
    a.process();
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO << "needed" << timer.elapsed();

    return app.exec();
}

--- a.cpp ---
#include "a.h"
#include "b.h"

A::A(QObject *parent) :
    QObject(parent),
    m_b(new B(this)){
    connect(m_b, &B::finished, this, &A::loopFinished);
}

A::~A() {
    if (m_b) {
        delete m_b;
        m_b = nullptr;
    }
}

void A::process() {
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO;

    //
    // start event-loop and wait for signal finished()
    //
    QEventLoop loop;
    connect(m_b, &B::finished, &loop, &QEventLoop::quit);

    //
    // use timeout
    //
    QTimer timer;
    timer.setSingleShot(true);
    connect(&timer, &QTimer::timeout, this, &A::timeout);
    connect(&timer, &QTimer::timeout, &loop, &QEventLoop::quit);
    timer.start(2000);

    //
    // exec loop
    //
    loop.exec();
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO;

    //
    // is timer active?
    //
    if (timer.isActive()) {
        qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO << "ok";
    } else {
        qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO << "timeout";
    }
}

void A::loopFinished() {
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO;
}

void A::timeout() {
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO;

    QTimer *timer = static_cast<QTimer *>(sender());
    if (timer) {
        qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO << "timeout";
    }
}

--- a.h ---
#pragma once

#include <QtCore>

class B;

class A : public QObject
{
    Q_OBJECT
public:
    explicit            A(QObject *parent = nullptr);
                        ~A();
    void                process();

private:
    B                   *m_b = nullptr;

private slots:
    void                loopFinished();
    void                timeout();
};

--- b.cpp ---
#include "b.h"

B::B(QObject *parent) :
    QObject(parent) {
    QTimer::singleShot(5000, this, &B::test);
}

B::~B() {

}

void B::test() {
    qDebug() << QDateTime::currentMSecsSinceEpoch() << Q_FUNC_INFO;
    emit finished();
}

--- b.h ---
#pragma once

#include <QtCore>

class B : public QObject
{
    Q_OBJECT
public:
    explicit            B(QObject *parent = nullptr);
                        ~B();
signals:
    void                finished();

private slots:
    void                test();
};