The earliest time a man can put on his Tefillin is called M’sh’yakir, which most opinions state is 45 minutes before sunrise (there are other opinions on when this time actually is.) A person cannot say the blessing on the Tefillin before this time. If a person needs to start praying before M’sh’yakir (i.e. needs to go to work or catch an airplane), he can start praying without wearing his Tefillin. After reciting Yishtabach, the person should make the blessing on his Tefillin and put it on (as long as it is now after M’sh’yakir). If the person is the Sh’liach Tzibbur (leader of the prayers), he should say the blessing and put on his Tefillin just before starting Yishtabach (so he can connect the prayer of Yishtabach to the Kaddish). Everyone else would first say Yishtabach on their own and then put on their Tefillin. Since the clocks will be changing this week, it is important that people who need to pray at early minyanim are aware of the different laws involved so their prayers are offered properly. A halachic authority should be consulted.