SFML Temporary speed boost implementation - c++

Question

in my SFML game, I'm trying to implement a Speed Boost option, however I don't quite know how to do it, here is a fragment of my code :
//Speed Boosts movement and collision
for(size_t i = 0; i < speedup.size(); i++){
speedup[i].shape.move(-0.2,0);
if(speedup[i].shape.getPosition().x <= 0 - speedup[i].shape.getGlobalBounds().width){
speedup.erase(speedup.begin()+i);
}
if(speedup[i].shape.getGlobalBounds().intersects(player.shape.getGlobalBounds())){
speedup.erase(speedup.begin()+i);
//SPEED UP HERE
}
Also, here's my player movement code:
//Player Movement
if(sf::Keyboard::isKeyPressed(sf::Keyboard::W))
player.shape.move(0,-0.5);
if(sf::Keyboard::isKeyPressed(sf::Keyboard::A))
player.shape.move(-0.5,0);
if(sf::Keyboard::isKeyPressed(sf::Keyboard::S))
player.shape.move(0,0.5);
if(sf::Keyboard::isKeyPressed(sf::Keyboard::D))
player.shape.move(0.5,0);
Now, I'd like, upon collision of the player with the speed boost sprite, for the players movement speed to be temporarily increased, however I don't quite know how to do it, should I use some fore loop and sf::Clock set the time of the boost? I also don't know how to change the movement speed temporarily.
I'd like more of a push in the right direction, than a complete code, so please give me hints how to realize that function
EDIT:
Proposed Speed boost implementation, it crashes:
if(speedup[i].shape.getGlobalBounds().intersects(player.shape.getGlobalBounds())){
speedup.erase(speedup.begin()+i);
float etime = clock.getElapsedTime().asSeconds();
while(etime<=10){
y_spd=2*y_spd;
x_spd=2*x_spd;
}
}
EDIT 2
I'm trying to figure out my timer so that it measures time from collision properly:
//Clock
sf::Clock dclock;
float dt = dclock.restart().asSeconds();
I declare this in my main(), I've tried doing it in many ways, none gives me proper time measurement.
//Speed Boost movement and collision
for(size_t i = 0; i < speedup.size(); i++){
speedup[i].shape.move(-5,0);
if(speedup[i].shape.getPosition().x <= 0 - speedup[i].shape.getGlobalBounds().width){
speedup.erase(speedup.begin()+i);
}
if(speedup[i].shape.getGlobalBounds().intersects(player.shape.getGlobalBounds())){
speedup.erase(speedup.begin()+i);
timer += dt;
}
}
//SPEED BOOSTING THE PLAYER
if(timer>=10){
y_spd=3;
x_spd=3;
timer = 0;
}